String.h conflicts with <string.h> on case insensitive filesystems

The Arduino API renamed "WString.h" to "String.h"
Given that "string.h" is a part of libc, and that most modern operating systems implement sort of "fuzzy" case-matching in their filesystems, this seems ripe for generating confusion.

And in fact, it seems to break builds when sketches have been imported into Atmel Studio 7, if they use the ArduinoAPI - when ipaddress.cpp is built as part of the core, it includes both and "String.h", and gets api/string.h for both of them, leaving the libc functions undefined:
```
Target "CoreBuild" in file "C:\Program Files (x86)\Atmel\Studio\7.0\Vs\Compiler.targets" from project "c:\users\rnovaes\Documents\Atmel Studio\7.0\ArduinoSketch7\ArduinoSketch7\ArduinoCore\ArduinoCore.cppproj" (target "Build" depends on it):
Using "RunCompilerTask" task from assembly "C:\Program Files (x86)\Atmel\Studio\7.0\Extensions\Application\AvrGCC.dll".
Task "RunCompilerTask"
Shell Utils Path C:\Program Files (x86)\Atmel\Studio\7.0\shellUtils
C:\Program Files (x86)\Atmel\Studio\7.0\shellUtils\make.exe all --jobs 4 --output-sync
Building file: ../src/core/api/IPAddress.cpp
Invoking: AVR8/GNU C Compiler : 5.4.0
"C:\Program Files (x86)\Atmel\Studio\7.0\toolchain\avr8\avr8-gnu-toolchain\bin\avr-g++.exe" -funsigned-char -funsigned-bitfields -DDEBUG -DF_CPU=16000000L -DARDUINO=10809 -DARDUINO_AVR_NANO_EVERY -DARDUINO_ARCH_AVR -DUSB_VID=0x2341 -DUSB_PID=0x0058 -DUSB_MANUFACTURER="\"Arduino LLC\"" -I"C:\Program Files (x86)\Atmel\Studio\7.0\Packs\atmel\ATmega_DFP\1.2.209\include" -I"..\include\core" -I"..\include\core\api" -I"..\include\core\api\deprecated" -I"..\include\core\api\deprecated-avr-comp\avr" -I"..\include\variants\nona4809" -Os -fno-threadsafe-statics -ffunction-sections -fdata-sections -fpack-struct -fshort-enums -g2 -w -mmcu=atmega4809 -B "C:\Program Files (x86)\Atmel\Studio\7.0\Packs\atmel\ATmega_DFP\1.2.209\gcc\dev\atmega4809" -c -std=gnu++11 -MD -MP -MF "src/core/api/IPAddress.d" -MT"src/core/api/IPAddress.d" -MT"src/core/api/IPAddress.o" -o "src/core/api/IPAddress.o" "../src/core/api/IPAddress.cpp"
In file included from ../src/core/api/IPAddress.cpp:21:0:
..\include\core\api/Print.h: In member function 'size_t Print::write(const char*)':
c:\users\rnovaes\Documents\Atmel Studio\7.0\ArduinoSketch7\ArduinoSketch7\ArduinoCore\include\core\api\Print.h(50,52): error: 'strlen' was not declared in this scope
return write((const uint8_t *)str, strlen(str));
^
../src/core/api/IPAddress.cpp: In constructor 'IPAddress::IPAddress(const uint8_t*)':
c:\users\rnovaes\Documents\Atmel Studio\7.0\ArduinoSketch7\ArduinoSketch7\ArduinoCore\src\core\api\IPAddress.cpp(43,59): error: 'memcpy' was not declared in this scope
memcpy(_address.bytes, address, sizeof(_address.bytes));
^
../src/core/api/IPAddress.cpp: In member function 'IPAddress& IPAddress::operator=(const uint8_t*)':
c:\users\rnovaes\Documents\Atmel Studio\7.0\ArduinoSketch7\ArduinoSketch7\ArduinoCore\src\core\api\IPAddress.cpp(90,59): error: 'memcpy' was not declared in this scope
memcpy(_address.bytes, address, sizeof(_address.bytes));
^
../src/core/api/IPAddress.cpp: In member function 'bool IPAddress::operator==(const uint8_t*) const':
c:\users\rnovaes\Documents\Atmel Studio\7.0\ArduinoSketch7\ArduinoSketch7\ArduinoCore\src\core\api\IPAddress.cpp(102,63): error: 'memcmp' was not declared in this scope
return memcmp(addr, _address.bytes, sizeof(_address.bytes)) == 0;
^
make: *** [src/core/api/IPAddress.o] Error 1
c:\users\rnovaes\Documents\Atmel Studio\7.0\ArduinoSketch7\ArduinoSketch7\ArduinoCore\Debug\Makefile(243,1): error: recipe for target 'src/core/api/IPAddress.o' failed
```

There is some discussion here: https://www.avrfreaks.net/forum/7-compilation-error-arduino-nano-every-sketch
The exact problem may be that AS7 adds `-I"..\include\core\api"` that isn't needed (or used in an Arduino IDE build), but it does illustrate the sort of confusion that can/will occur.

Start by inspecting src/core/api/IPAddress.cpp, include/core/api/Print.h, and the conflicting String.h and includes under the Atmel Studio 7 include paths. Reproduce the reported CoreBuild failure and determine how the headers are being resolved. Done means the affected build resolves both headers correctly and the libc functions strlen, memcpy, and memcmp are available.

Written by the indexing model from the issue text.