Use getauxval on Linux if available.

--- SDL2-2.0.22/src/cpuinfo/SDL_cpuinfo.c.old	2022-01-08 02:29:52.000000000 +0000
+++ SDL2-2.0.22/src/cpuinfo/SDL_cpuinfo.c	2025-04-27 18:58:12.097867624 +0000
@@ -113,7 +113,7 @@
 #define CPU_HAS_AVX512F (1 << 12)
 #define CPU_HAS_ARM_SIMD (1 << 13)
 
-#if SDL_ALTIVEC_BLITTERS && HAVE_SETJMP && !__MACOSX__ && !__OpenBSD__ && !__FreeBSD__
+#if SDL_ALTIVEC_BLITTERS && HAVE_SETJMP && !__MACOSX__ && !__OpenBSD__ && !__FreeBSD__ && !__linux__
 /* This is the brute force way of detecting instruction sets...
    the idea is borrowed from the libmpeg2 library - thanks!
  */
@@ -333,6 +333,8 @@
     elf_aux_info(AT_HWCAP, &cpufeatures, sizeof(cpufeatures));
     altivec = cpufeatures & PPC_FEATURE_HAS_ALTIVEC;
     return altivec;
+#elif defined(__linux__) && defined(__powerpc__) && HAVE_GETAUXVAL
+    altivec = getauxval(AT_HWCAP) & PPC_FEATURE_HAS_ALTIVEC;
 #elif SDL_ALTIVEC_BLITTERS && HAVE_SETJMP
     void (*handler) (int sig);
     handler = signal(SIGILL, illegal_instruction);