checkpatch: Don't warn about if ((status = _xbegin()) == _XBEGIN_STARTED)

Writing _xbegin which is like setjmp in a if is very natural.
Stop checkpatch's whining about this.

Cc: apw@canonical.com
Signed-off-by: Andi Kleen <ak@linux.intel.com>

scripts/checkpatch.pl

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index b954de5..21a6d62 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -2840,7 +2840,10 @@
 		    $line =~ /\b(?:if|while|for)\s*\(/ && $line !~ /^.\s*#/) {
 			my ($s, $c) = ($stat, $cond);
 
-			if ($c =~ /\bif\s*\(.*[^<>!=]=[^=].*/s) {
+			# if ((status = _xbegin()) == _XBEGIN_STARTED) is natural,
+			# so don't warn about this case.
+			if ($c =~ /\bif\s*\(.*[^<>!=]=[^=].*/s &&
+			    $c !~ /_xbegin/) {
 				ERROR("ASSIGN_IN_IF",
 				      "do not use assignment in if condition\n" . $herecurr);
 			}