Restrict x86 mnemonic to x86-64

This resolves an issue where setting the assert config to breakpoint
on ARM will cause the build to fail with an accurate but unhelpful
compiler error.

This restricts the mnemonic to x86-64 architectures, and provides a
more explanatory error.

Addresses issue: #2890

Signed-off-by: Will Marone <Will.Marone@amd.com>

Author: wmaroneAMD

os_stub/debuglib/debuglib.c

@@ -37,9 +37,10 @@ void libspdm_debug_assert(const char *file_name, size_t line_number, const char
 #elif (LIBSPDM_DEBUG_LIBSPDM_ASSERT_CONFIG == LIBSPDM_DEBUG_LIBSPDM_ASSERT_BREAKPOINT)
 #if defined(_MSC_EXTENSIONS)
     __debugbreak();
-#endif
-#if defined(__GNUC__)
+#elif defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
     __asm__ __volatile__ ("int $3");
+#else
+#error Breakpoint asserts are not available on this architecture and/or compiler
 #endif
 #elif (LIBSPDM_DEBUG_LIBSPDM_ASSERT_CONFIG == LIBSPDM_DEBUG_LIBSPDM_ASSERT_EXIT)
     exit(1);