scripts/checkpatch: Check for patches adding #defines for libc APIs

All code in the Zephyr core must use only the Zephyr C library API
according to rules A.4 and A.5. Such code is not permitted to request API
extensions from the C library via any of the API request mechanisms.

This addition to checkpatch.pl verifies that patches don't #define
any of these:

	__STRICT_ANSI__
	_POSIX_SOURCE
	_POSIX_C_SOURCE
	_XOPEN_SOURCE
	_ISOC99_SOURCE
	_ISOC11_SOURCE
	_ATFILE_SOURCE
	_GNU_SOURCE
	_BSD_SOURCE
	_SVID_SOURCE
	_DEFAULT_SOURCE

Reference: #49922

Signed-off-by: Keith Packard <keithp@keithp.com>

scripts/checkpatch.pl

@@ -592,6 +592,20 @@ sub hash_show_words {
 	["__ATTR", 2],
 );
 
+our $api_defines = qr{(?x:
+	_POSIX_SOURCE|
+	_POSIX_C_SOURCE|
+	_XOPEN_SOURCE|
+	_XOPEN_SOURCE_EXTENDED|
+	_ISOC99_SOURCE|
+	_ISOC11_SOURCE|
+	_ATFILE_SOURCE|
+	_GNU_SOURCE|
+	_BSD_SOURCE|
+	_SVID_SOURCE|
+	_DEFAULT_SOURCE
+)};
+
 my $word_pattern = '\b[A-Z]?[a-z]{2,}\b';
 
 #Create a search pattern for all these functions to speed up a loop below
@@ -6527,6 +6541,13 @@ sub process {
 			}
 		}
 
+# check for #defines of various API specifying things like _POSIX_C_SOURCE
+
+		if ($line =~ /#\s*define\s+$api_defines/) {
+			ERROR("API_DEFINE",
+			      "do not specify a non-Zephyr API for libc\n" . "$here$rawline\n");
+		}
+
 # check for IS_ENABLED() without CONFIG_<FOO> ($rawline for comments too)
 		if ($rawline =~ /\bIS_ENABLED\s*\(\s*(\w+)\s*\)/ && $1 !~ /^CONFIG_/) {
 			WARN("IS_ENABLED_CONFIG",