MSVC and GNU compilers use different attributes for noinline.
Abstract away compiler differences.

__cdecl is not defined by default on GNU compilers.

__sync_swap doesn't exist on GNU. Replacing with __atomic_exchange_n
which is universally available.

A pointer value is usually unsigned long on most platforms.
Casting it to integer causes signedness issues. Use size_t
to be efficient on all 32 and 64 bit architectures.

Correct error statement. GNU G++ is picky about the string
following the error statement with ' character in it. It needs
to be enclosed with double quotes.

Seeing these warnings with GNU G++ compiler

src/pal/src/sync/cs.cpp: In function ‘void CorUnix::InternalInitializeCriticalSectionAndSpinCount(PCRITICAL_SECTION, DWORD, bool)’:
src/pal/src/sync/cs.cpp:630:48: warning: converting to non-pointer type ‘SIZE_T {aka long unsigned int}’ from NULL [-Wconversion-null]
         pPalCriticalSection->OwningThread      = NULL;
                                                ^
src/pal/src/sync/cs.cpp: In function ‘void CorUnix::InternalLeaveCriticalSection(CorUnix::CPalThread*, _CRITICAL_SECTION*)’:
src/pal/src/sync/cs.cpp:880:43: warning: converting to non-pointer type ‘SIZE_T {aka long unsigned int}’ from NULL [-Wconversion-null]
         pPalCriticalSection->OwningThread = NULL;
                                           ^

GNU compiler doesn't support optnone attribute.

pal/src/exception/seh-unwind.cpp:449:77: warning: ‘optnone’ attribute directive ignored [-Wattributes]

GNU compiler doesn't have an intrinsic for these. Open code them
using the provided implementation.

/usr/include/string.h:43:28: error: declaration of ‘void* memcpy(void*, const void*, size_t) throw ()’ has a different exception specifier
        size_t __n) __THROW __nonnull ((1, 2));