Fix uncaught-exception.test. (llvm#146190)

See llvm#125924
To match a literal plus sign, it must be escaped with a backslash (`\`).

Author: qinkunbao

compiler-rt/test/fuzzer/uncaught-exception.test

@@ -8,4 +8,4 @@ RUN: %cpp_compiler %S/UncaughtException.cpp -o %t-UncaughtException
 # For example, msvc fails with 'uncaught C++ exception'. So the error we check depends on the compiler target.
 RUN: not %run %t-UncaughtException 2>&1 | FileCheck %s
 
-CHECK: ERROR: libFuzzer: {{deadly signal|uncaught C++ exception}}
+CHECK: ERROR: libFuzzer: {{deadly signal|uncaught C\+\+ exception}}