[scudo][standalone] Fix build for Fuchsia

[cryptoad]

Summary

Recent changes have introduced code that fails to build on Fuchsia.
This fixes the build by adding non-Linux functions alternatives.

[cryptoad]

Roland committed his change for the issue, this is no longer needed.

compiler-rt/lib/scudo/standalone/memtag.h

inline uint8_t extractTag(uptr Ptr) {
   (void)Ptr;
   UNREACHABLE("memory tagging not supported");
 }
 
 #endif
 
 #if defined(__aarch64__)
 
+#if SCUDO_LINUX
 inline bool systemSupportsMemoryTagging() {
 #ifndef HWCAP2_MTE
 #define HWCAP2_MTE (1 << 18)
 #endif
   return getauxval(AT_HWCAP2) & HWCAP2_MTE;
 }
 
 inline bool systemDetectsMemoryTagFaultsTestOnly() {
 #ifndef PR_GET_TAGGED_ADDR_CTRL
 #define PR_GET_TAGGED_ADDR_CTRL 56
 #endif
 #ifndef PR_MTE_TCF_SHIFT
 #define PR_MTE_TCF_SHIFT 1
 #endif
 #ifndef PR_MTE_TCF_NONE
 #define PR_MTE_TCF_NONE (0UL << PR_MTE_TCF_SHIFT)
 #endif
 #ifndef PR_MTE_TCF_MASK
 #define PR_MTE_TCF_MASK (3UL << PR_MTE_TCF_SHIFT)
 #endif
   return (static_cast<unsigned long>(
               prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0)) &
           PR_MTE_TCF_MASK) != PR_MTE_TCF_NONE;
 }
+#else
+inline bool systemSupportsMemoryTagging() { return false; }
+inline bool systemDetectsMemoryTagFaultsTestOnly() { return false; }
+#endif // SCUDO_LINUX
 
 inline void disableMemoryTagChecksTestOnly() {
   __asm__ __volatile__(".arch_extension mte; msr tco, #1");
 }
 
 inline void enableMemoryTagChecksTestOnly() {
   __asm__ __volatile__(".arch_extension mte; msr tco, #0");
 }