GCC Module mapper (file based)

GCC Module mapper (file based)

[Arthur Laurent]

Hello, i'm a XMake contributor and i'm trying to improve our GCC 
modulemap support

i'm currently facing an issue with the path handling (i think so) of 
headerunits, i don't know if i did anything wrong

i'm generating a modulemap file like

```
root F:/repos/xmake/tests/projects/c++/modules/user_headerunit

F:/repos/xmake/tests/projects/c++/modules/user_headerunit/src/header.hpp 
build/.gens/user_headerunit/mingw/x86_64/release/rules/bmi/cache/headerunits/header.hpp.gcm

```

but when i supply this modulemap file to gcc to build the headerunit i'm 
getting:

```

x86_64-w64-mingw32-g++ -c -m64 -std=c++20 -fmodules-ts 
-D_GLIBCXX_USE_CXX11_ABI=0 
-IF:\repos\xmake\tests\projects\c++\modules\user_headerunit\src 
-fmodule-mapper=F:\msys64\tmp\.xmake\231130\modulemap.txt 
-fmodule-header=user -fmodule-only -xc++-header -c -o 
build\.gens\user_headerunit\mingw\x86_64\release\rules\bmi\cache\headerunits\header.hpp.gcm 
header.hpp

F:\repos\xmake\tests\projects\c++\modules\user_headerunit\src/header.hpp: 
error: unknown Compiled Module Interface: no such module

F:\repos\xmake\tests\projects\c++\modules\user_headerunit\src/header.hpp:5: 
confused by earlier errors, bailing out

```

any idea on how to fix this ?