tests/Garm64-test-sve-signal: check that SVE is present before running tests

If the compiler supports -march=armv8-a+sve then those options are used
to build this test, but all that needs is a sufficiently new compiler.

This then results in the __ARM_FEATURE_SVE check always passing, because
SVE is explicitly enabled.

However it's perfectly possible for the compiler to support +sve but the
machine running the code to not, which results with the test crashing
with "Illegal instruction".

Handle this case by checking HWCAP for SVE support, and skipping the
test unless we know it is available.  This check is Linux-specific at
present, but the logic is easily extended.

Signed-off-by: Ross Burton <ross.burton@arm.com>

tests/Garm64-test-sve-signal.c

@@ -9,11 +9,16 @@
 #include <libunwind.h>
 #include <signal.h>
 #include <stdio.h>
+#include <stdbool.h>
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
 #include <unistd.h>
 
+#if defined(__linux__)
+#include <sys/auxv.h>
+#endif
+
 int64_t z[100];
 
 void signal_handler(int signum)
@@ -96,8 +101,22 @@ int64_t square(svint64_t z0)
   return res;
 }
 
+bool has_sve(void) {
+#if defined(__linux__)
+  return (getauxval(AT_HWCAP) & HWCAP_SVE) ? true : false;
+#else
+  printf("Cannot determine if SVE is present, assuming it is not\n");
+  return false;
+#endif
+}
+
 int main()
 {
+  if (!has_sve()) {
+    printf("SVE not available, skipping\n");
+    return 77;
+  }
+
   signal(SIGUSR1, signal_handler);
   for (unsigned int i = 0; i < sizeof(z) / sizeof(z[0]); ++i)
     z[i] = rand();