Annotate ColoredPrintf with the format attribute and fix bugs.

googletest doesn't currently build with clang's very aggressive
-Wformat-nonliteral warning. It requires that all non-literal format
strings come from the argument of a function annotated with a compatible
format attribute.

Fixing that reports that ColoredPrintf's callers weren't passing the
normal -Wformat warning. Some messages were passed directly into the
format string rather than via "%s".

googletest/include/gtest/internal/gtest-port.h

@@ -874,6 +874,23 @@ using ::std::tuple_size;
 # define GTEST_ATTRIBUTE_UNUSED_
 #endif
 
+// Use this annotation before a function that takes a printf format string.
+#if defined(__GNUC__) && !defined(COMPILER_ICC)
+# if defined(__MINGW_PRINTF_FORMAT)
+// MinGW has two different printf implementations. Ensure the format macro
+// matches the selected implementation. See
+// https://sourceforge.net/p/mingw-w64/wiki2/gnu%20printf/.
+#  define GTEST_ATTRIBUTE_PRINTF_(string_index, first_to_check) \
+       __attribute__((__format__(__MINGW_PRINTF_FORMAT, string_index, \
+                                 first_to_check)))
+# else
+#  define GTEST_ATTRIBUTE_PRINTF_(string_index, first_to_check) \
+       __attribute__((__format__(__printf__, string_index, first_to_check)))
+# endif
+#else
+# define GTEST_ATTRIBUTE_PRINTF_(string_index, first_to_check)
+#endif
+
 // A macro to disallow operator=
 // This should be used in the private: declarations for a class.
 #define GTEST_DISALLOW_ASSIGN_(type)\