Core code should compile without warnings.

As I mentioned on the memory corruption issue, as a general practice, I don't want to see any compiler warnings, in my builds, even with the full or all warnings option turned on. Often times Warnings give you a hint on what might be wrong.

But your mind gets unsensitized to it, when you see them with every build. So you might miss ones that actually might help localize an issue.

With the current board release, I see warnings in at least two of the source files:
```
"C:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\tools\\arm-none-eabi-gcc\\7-2017q4/bin/arm-none-eabi-g++" -c -Wall -Wextra -Os -g3 -fno-use-cxa-atexit -fno-rtti -fno-exceptions -MMD -nostdlib -DF_CPU=48000000 -DNO_USB -DBACKTRACE_SUPPORT -DARDUINO_UNOR4_WIFI -MMD -std=gnu++17 -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -fsigned-char -ffunction-sections -fdata-sections -fmessage-length=0 -fno-builtin -DARDUINO=10607 "-DPROJECT_NAME=\"C:\\Users\\kurte\\AppData\\Local\\Temp\\arduino\\sketches\\BD525D585FBF6679F28F92809D7A82B2/string_memory_corrupt.ino\"" -DARDUINO_UNOWIFIR4 -DARDUINO_ARCH_RENESAS_UNO -DARDUINO_ARCH_RENESAS -DARDUINO_FSP -D_XOPEN_SOURCE -mthumb "@C:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.0.2\\variants\\UNOWIFIR4/defines.txt" -DCFG_TUSB_MCU=OPT_MCU_RAXXX "-IC:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.0.2/cores/arduino/tinyusb" "-IC:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.0.2\\cores\\arduino/api/deprecated" "-IC:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.0.2\\cores\\arduino/api/deprecated-avr-comp" "-IC:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.0.2\\cores\\arduino" "-IC:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.0.2\\variants\\UNOWIFIR4" "-iprefixC:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.0.2" "@C:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.0.2\\variants\\UNOWIFIR4/includes.txt" "C:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.0.2\\cores\\arduino\\time.cpp" -o "C:\\Users\\kurte\\AppData\\Local\\Temp\\arduino\\sketches\\BD525D585FBF6679F28F92809D7A82B2\\core\\time.cpp.o"
C:\Users\kurte\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.0.2\cores\arduino\cm_backtrace\cm_backtrace.c: In function 'cm_backtrace_init':
C:\Users\kurte\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.0.2\cores\arduino\cm_backtrace\cm_backtrace.c:144:13: warning: assignment discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
fw_name = firmware_name;
^
C:\Users\kurte\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.0.2\cores\arduino\cm_backtrace\cm_backtrace.c:145:12: warning: assignment discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
hw_ver = hardware_ver;
^
C:\Users\kurte\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.0.2\cores\arduino\cm_backtrace\cm_backtrace.c:146:12: warning: assignment discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
sw_ver = software_ver;
```
And:
```
"C:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\tools\\arm-none-eabi-gcc\\7-2017q4/bin/arm-none-eabi-g++" -c -Wall -Wextra -Os -g3 -fno-use-cxa-atexit -fno-rtti -fno-exceptions -MMD -nostdlib -DF_CPU=48000000 -DNO_USB -DBACKTRACE_SUPPORT -DARDUINO_UNOR4_WIFI -MMD -std=gnu++17 -mcpu=cortex-m4 -mfloat-abi=hard -mfpu=fpv4-sp-d16 -fsigned-char -ffunction-sections -fdata-sections -fmessage-length=0 -fno-builtin -DARDUINO=10607 "-DPROJECT_NAME=\"C:\\Users\\kurte\\AppData\\Local\\Temp\\arduino\\sketches\\BD525D585FBF6679F28F92809D7A82B2/string_memory_corrupt.ino\"" -DARDUINO_UNOWIFIR4 -DARDUINO_ARCH_RENESAS_UNO -DARDUINO_ARCH_RENESAS -DARDUINO_FSP -D_XOPEN_SOURCE -mthumb "@C:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.0.2\\variants\\UNOWIFIR4/defines.txt" -DCFG_TUSB_MCU=OPT_MCU_RAXXX "-IC:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.0.2/cores/arduino/tinyusb" "-IC:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.0.2\\cores\\arduino/api/deprecated" "-IC:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.0.2\\cores\\arduino/api/deprecated-avr-comp" "-IC:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.0.2\\cores\\arduino" "-IC:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.0.2\\variants\\UNOWIFIR4" "-iprefixC:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.0.2" "@C:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.0.2\\variants\\UNOWIFIR4/includes.txt" "C:\\Users\\kurte\\AppData\\Local\\Arduino15\\packages\\arduino\\hardware\\renesas_uno\\1.0.2\\cores\\arduino\\usb\\USB.cpp" -o "C:\\Users\\kurte\\AppData\\Local\\Temp\\arduino\\sketches\\BD525D585FBF6679F28F92809D7A82B2\\core\\usb\\USB.cpp.o"
C:\Users\kurte\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.0.2\cores\arduino\IRQManager.cpp: In member function 'bool IRQManager::addPeripheral(Peripheral_t, void*)':
C:\Users\kurte\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.0.2\cores\arduino\IRQManager.cpp:345:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
if (irqcfg->first_irq_number != FSP_INVALID_VECTOR) {
C:\Users\kurte\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.0.2\cores\arduino\IRQManager.cpp:408:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
if (irqcfg->first_irq_number != FSP_INVALID_VECTOR) {
C:\Users\kurte\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.0.2\cores\arduino\IRQManager.cpp: In member function 'void IRQManager::set_canfd_error_link_event(int, int)':
C:\Users\kurte\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.0.2\cores\arduino\IRQManager.cpp:1662:49: warning: unused parameter 'li' [-Wunused-parameter]
void IRQManager::set_canfd_error_link_event(int li, int ch)
^~
C:\Users\kurte\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.0.2\cores\arduino\IRQManager.cpp:1662:57: warning: unused parameter 'ch' [-Wunused-parameter]
void IRQManager::set_canfd_error_link_event(int li, int ch)
^~
C:\Users\kurte\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.0.2\cores\arduino\IRQManager.cpp: In member function 'void IRQManager::set_canfd_rx_link_event(int, int)':
C:\Users\kurte\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.0.2\cores\arduino\IRQManager.cpp:1677:46: warning: unused parameter 'li' [-Wunused-parameter]
void IRQManager::set_canfd_rx_link_event(int li, int ch)
^~
C:\Users\kurte\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.0.2\cores\arduino\IRQManager.cpp:1677:54: warning: unused parameter 'ch' [-Wunused-parameter]
void IRQManager::set_canfd_rx_link_event(int li, int ch)
^~
C:\Users\kurte\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.0.2\cores\arduino\IRQManager.cpp: In member function 'void IRQManager::set_canfd_tx_link_event(int, int)':
C:\Users\kurte\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.0.2\cores\arduino\IRQManager.cpp:1692:46: warning: unused parameter 'li' [-Wunused-parameter]
void IRQManager::set_canfd_tx_link_event(int li, int ch)
^~
C:\Users\kurte\AppData\Local\Arduino15\packages\arduino\hardware\renesas_uno\1.0.2\cores\arduino\IRQManager.cpp:1692:54: warning: unused parameter 'ch' [-Wunused-parameter]
void IRQManager::set_canfd_tx_link_event(int li, int ch)
^~
```
My quick look through I don't see anything obvious that is impacting the memory corruption bug, but...

Start by rebuilding the ArduinoCore-renesas core with -Wall and -Wextra, then inspect the warning sites named in cm_backtrace.c and IRQManager.cpp. Address the discarded-qualifier, signed/unsigned comparison, and unused-parameter warnings shown in the issue. Done means the core build produces no compiler warnings with the full warning options enabled.

Written by the indexing model from the issue text.