[UBSan] Increase robustness of tests

[yln]

Summary

These UBSan tests assert the absence of runtime errors via count 0,
which means "expect no output". This fails the test unnecessarily in
some environments (e.g., iOS simulator in our case). Alter the test to
be a bit more specific and "expect no error" instead of "expect no
output".

rdar://65503408

[vsk]

Thanks for fixing this!

compiler-rt/test/ubsan/TestCases/Misc/nonnull.cpp

 // RUN: %clangxx -fsanitize=returns-nonnull-attribute -w %s -O3 -o %t
-// RUN: %run %t foo 2>&1 | count 0
+// RUN: %run %t foo 2>&1 | FileCheck %s --check-prefix=NOERROR --allow-empty --implicit-check-not='runtime error'
 // RUN: %run %t 2>&1 | FileCheck %s
 // RUN: %clangxx -fsanitize=returns-nonnull-attribute -fno-sanitize-recover=returns-nonnull-attribute -w %s -O3 -o %t.abort
 // RUN: not %run %t.abort &> /dev/null
 
 __attribute__((returns_nonnull)) char *foo(char *a);
 
 char *foo(char *a) {
   // CHECK: nonnull.cpp:[[@LINE+2]]:3: runtime error: null pointer returned from function declared to never return null
int main(int argc, char **argv) {
   bar(5, a);
 
   // ... but not a second time.
   // CHECK-NOT: runtime error
   bar(5, a);
 
   return 0;
 }
+
+// NOERROR-NOT: runtime error

compiler-rt/test/ubsan/TestCases/Misc/nullability.c

 // UNSUPPORTED: android
 // RUN: %clang -w -fsanitize=nullability-arg,nullability-assign,nullability-return %s -O3 -o %t
-// RUN: %run %t foo 2>&1 | count 0
+// RUN: %run %t foo 2>&1 | FileCheck %s --check-prefix=NOERROR --allow-empty --implicit-check-not='runtime error'
 // RUN: %run %t 2>&1 | FileCheck %s
 
 // RUN: echo "nullability-arg:nullability.c" > %t.supp
 // RUN: echo "nullability-return:nullability.c" >> %t.supp
 // RUN: echo "nullability-assign:nullability.c" >> %t.supp
 // RUN: env UBSAN_OPTIONS=suppressions='"%t.supp"' %run %t 2>&1 | FileCheck -allow-empty -check-prefix=SUPPRESS %s
 // SUPPRESS-NOT: runtime error
 
#line 1000
   nonnull_arg(p);
   nonnull_assign1(p);
   nonnull_assign2(p);
   nonnull_assign3(p);
   nonnull_init1(p);
   nonnull_init2(p);
   return 0;
 }
+
+// NOERROR-NOT: runtime error