x86emul/test: improve failure location identification for FMA sub-test

When some FMA set of insns is included in the base instruction set (XOP,
AVX512F, and AVX512-FP16 at present), simd_test() simply invokes
fma_test(), negating its return value. In case of a failure this would
yield a value close to 4G, which doesn't lend itself to easy
identification of the failing test case. Recognize the case in
simd_check_regs() and emit alternative output identifying FMA.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

tools/tests/x86_emulator/test_x86_emulator.c

@@ -259,7 +259,10 @@ static bool simd_check_regs(const struct cpu_user_regs *regs)
 {
     if ( !regs->eax )
         return true;
-    printf("[line %u] ", (unsigned int)regs->eax);
+    if ( (int)regs->eax > 0 )
+        printf("[line %u] ", (unsigned int)regs->eax);
+    else
+        printf("[FMA line %u] ", (unsigned int)-regs->eax);
     return false;
 }