crypto/bn/asm/x86_64-mont*.pl: add missing clang detection.

Reviewed-by: NRich Salz <rsalz@openssl.org>

crypto/bn/asm/x86_64-mont.pl

@@ -68,6 +68,11 @@ if (!$addx && $win64 && ($flavour =~ /masm/ || $ENV{ASM} =~ /ml64/) &&
 	$addx = ($1>=12);
 }
 
+if (!$addx && `$ENV{CC} -v 2>&1` =~ /(^clang version|based on LLVM) ([3-9])\.([0-9]+)/) {
+	my $ver = $2 + $3/100.0;	# 3.1->3.01, 3.10->3.10
+	$addx = ($ver>=3.03);
+}
+
 # int bn_mul_mont(
 $rp="%rdi";	# BN_ULONG *rp,
 $ap="%rsi";	# const BN_ULONG *ap,

crypto/bn/asm/x86_64-mont5.pl

@@ -53,6 +53,11 @@ if (!$addx && $win64 && ($flavour =~ /masm/ || $ENV{ASM} =~ /ml64/) &&
 	$addx = ($1>=12);
 }
 
+if (!$addx && `$ENV{CC} -v 2>&1` =~ /(^clang version|based on LLVM) ([3-9])\.([0-9]+)/) {
+	my $ver = $2 + $3/100.0;	# 3.1->3.01, 3.10->3.10
+	$addx = ($ver>=3.03);
+}
+
 # int bn_mul_mont_gather5(
 $rp="%rdi";	# BN_ULONG *rp,
 $ap="%rsi";	# const BN_ULONG *ap,