pw_assert/libc_assert: Correct macro typo

Corrects a typo which meant the define check was looking for
__STDC_VERSION to be defined instead of __STDC_VERSION__.

Also cleans up the use of defined for legibility.

Change-Id: I3fde1222ff5d7c5893472b72bf593db4cae72cf8
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/131792
Pigweed-Auto-Submit: Ewout van Bekkum <ewout@google.com>
Reviewed-by: Wyatt Hepler <hepler@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>

pw_assert/public/pw_assert/internal/libc_assert.h

@@ -27,16 +27,16 @@ extern "C++" {
 #endif  // __cplusplus
 
 // Provide static_assert() on >=C11
-#if (defined __USE_ISOC11 ||                                   \
-     defined __STDC_VERSION && __STDC_VERSION__ >= 201112L) && \
-    !defined __cplusplus
+#if (defined(__USE_ISOC11) ||                                       \
+     defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 201112L)) && \
+    !defined(__cplusplus)
 #define static_assert _Static_assert
 #endif  // C11 or newer
 
 // Provide assert()
 #undef assert
-#if defined NDEBUG  // Required by ANSI C standard.
+#if defined(NDEBUG)  // Required by ANSI C standard.
 #define assert(condition) ((void)0)
 #else
 #define assert(condition) PW_ASSERT(condition)
-#endif  // defined NDEBUG
+#endif  // defined(NDEBUG)