fix(warnings): silence two -Wall/-Wextra warnings on the MinGW build

[woolcoxm]

What

A clean make glm on MinGW emitted exactly two -Wall -Wextra warnings. Both are real; this silences them.

The two warnings

1. compat.h:240 — ignoring '#pragma comment ' [-Wunknown-pragmas]

#pragma comment(lib, "psapi.lib")

This is an MSVC linker directive. MinGW/GCC doesn't understand it and warns. Guarded with #ifdef _MSC_VER — MinGW already links psapi via -lpsapi (in the Makefile / .build-config), and MSVC keeps the pragma.

2. glm.c:1210 — 'g_numa_nodes' defined but not used [-Wunused-variable]

g_numa_nodes is only read/written inside #ifdef __linux__ blocks (numa_slab_bind, numa_init). On every non-Linux build it's a file-scope static that nothing references → unused-variable warning. Moved the definition under the same __linux__ guard:

#ifdef __linux__
static int g_numa_nodes=0;      /* only touched under __linux__; off-Linux NUMA is a no-op */
#endif

Off-Linux numa_slab_bind / numa_init are already full no-ops (they (void) their args and return), so nothing references the variable there.

Verification

rm -f *.o glm.exe && make glm   # 0 warnings, 0 errors, binary builds

Behavior is unchanged on Linux (the variable is identical there) and on MSVC (the pragma is unchanged there).