Allow --strict-warnings with the icc compiler as well

Reviewed-by: NTim Hudson <tjh@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4250)

Configure

@@ -1323,8 +1323,8 @@ if (defined($config{api})) {
 if ($strict_warnings)
 	{
 	my $wopt;
-	die "ERROR --strict-warnings requires gcc or clang"
-            unless $ecc eq 'gcc' || $ecc eq 'clang';
+	die "ERROR --strict-warnings requires gcc, clang or icc"
+            unless $ecc eq 'gcc' || $ecc eq 'clang' || $ecc eq 'icc';
 	foreach $wopt (split /\s+/, $gcc_devteam_warn)
 		{
 		$config{cflags} .= " $wopt" unless ($config{cflags} =~ /(?:^|\s)$wopt(?:\s|$)/)