test: add test for C++ applications

[alfredh]

Proposal to compile a C++ application to test libre api.

There are some build errors for ARM64-Windows:

FAILED: test/CMakeFiles/retest.dir/cplusplus.cpp.obj 
C:\PROGRA~1\MICROS~2\2022\ENTERP~1\VC\Tools\MSVC\1442~1.344\bin\Hostx64\arm64\cl.exe  /nologo /TP -DARCH=\"AMD64\" -DHAVE_ATOMIC -DHAVE_IO_H -DHAVE_PQOS_FLOWID -DHAVE_QOS_FLOWID -DHAVE_SELECT -DHAVE_UNIXSOCK=1 -DOS=\"Windows\" -DRE_VERSION=\"3.18.0\" -DVER_MAJOR=3 -DVER_MINOR=18 -DVER_PATCH=0 -DWIN32 -D_CRT_SECURE_NO_WARNINGS -D_GNU_SOURCE -D_WIN32_WINNT=0x0600 -Dretest_EXPORTS -ID:\a\re\re\test\. -ID:\a\re\re\include /DWIN32 /D_WINDOWS /EHsc /Ob0 /Od /RTC1 -MDd -Zi /W3 /showIncludes /Fotest\CMakeFiles\retest.dir\cplusplus.cpp.obj /Fdtest\CMakeFiles\retest.dir\ /FS -c D:\a\re\re\test\cplusplus.cpp
D:\a\re\re\include\re_atomic.h(602): error C2664: 'char __iso_volatile_load8(volatile const char *)': cannot convert argument 1 from 'const unsigned char *' to 'volatile const char *'
D:\a\re\re\include\re_atomic.h(602): note: Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or parenthesized function-style cast
C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.42.34433\include\intrin0.inl.h(273): note: see declaration of '__iso_volatile_load8'
D:\a\re\re\include\re_atomic.h(602): note: while trying to match the argument list '(const unsigned char *)'
D:\a\re\re\include\re_atomic.h(605): error C2664: 'short __iso_volatile_load16(volatile const short *)': cannot convert argument 1 from 'const unsigned short *' to 'volatile const short *'
D:\a\re\re\include\re_atomic.h(605): note: Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or parenthesized function-style cast
C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.42.34433\include\intrin0.inl.h(270): note: see declaration of '__iso_volatile_load16'
D:\a\re\re\include\re_atomic.h(605): note: while trying to match the argument list '(const unsigned short *)'
D:\a\re\re\include\re_atomic.h(608): error C2664: 'int __iso_volatile_load32(volatile const int *)': cannot convert argument 1 from 'const unsigned int *' to 'volatile const int *'
D:\a\re\re\include\re_atomic.h(608): note: Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or parenthesized function-style cast
C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.42.34433\include\intrin0.inl.h(271): note: see declaration of '__iso_volatile_load32'
D:\a\re\re\include\re_atomic.h(608): note: while trying to match the argument list '(const unsigned int *)'
D:\a\re\re\include\re_atomic.h(611): error C2664: '__int64 __iso_volatile_load64(volatile const __int64 *)': cannot convert argument 1 from 'const unsigned __int64 *' to 'volatile const __int64 *'
D:\a\re\re\include\re_atomic.h(611): note: Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or parenthesized function-style cast
C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.42.34433\include\intrin0.inl.h(272): note: see declaration of '__iso_volatile_load64'
D:\a\re\re\include\re_atomic.h(611): note: while trying to match the argument list '(const unsigned __int64 *)'
ninja: build stopped: subcommand failed.

[alfredh]

@sreimers could you please review this ?

There is at least one fix in re_atomic.h that we could merge ...

[sreimers]

There is at least one fix in re_atomic.h that we could merge ...

Can you create a extra PR for the re_atomic.h changes.

[sreimers]

Looks good to me

[alfredh]

this was my proposal to add C++ to retest which discovered one compile error.

Is there agreement to add C++ to retest ?