Set higher timeouts for Misc-C++ on AArch64

When running the test-suite on AArch64 at -O0, we sometimes get timeouts
in stepanov-v1p2. It usually takes more than 450s to run it, and the
threshold is only 500s. Increase it to 750s.

We're modifying the Makefiles because this is what the AArch64 buildbots
currently use.

Similar to r305671, which increased the timeouts for PAQ8p and SciMark-2.

llvm-svn: 308165
diff --git a/SingleSource/Benchmarks/Misc-C++/Makefile b/SingleSource/Benchmarks/Misc-C++/Makefile
index 2080f0a..d93aa20 100644
--- a/SingleSource/Benchmarks/Misc-C++/Makefile
+++ b/SingleSource/Benchmarks/Misc-C++/Makefile
@@ -8,6 +8,12 @@
 ifndef SMALL_PROBLEM_SIZE
 XCORE_TARGET_NEEDS_MEMORY := 128
 endif
+else
+ifeq ($(ARCH),AArch64)
+# On AArch64 at -O0 we get very close to 500s and sometimes we go over the
+# threshold. Set it to a more comfortable value.
+RUNTIMELIMIT := 750
+endif
 endif
 
 include $(LEVEL)/SingleSource/Makefile.singlesrc