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.

まず src/core/api/IPAddress.cpp、include/core/api/Print.h、および Atmel Studio 7 の include パスにある競合する String.h と の include を調査します。報告された CoreBuild の失敗を再現し、ヘッダーがどのように解決されているかを特定します。影響を受けるビルドで両方のヘッダーが正しく解決され、libc 関数 strlen、memcpy、memcpy が利用可能になれば完了です。

索引モデルが issue の本文から書いたものです。