support old as

/tmp/ccBWbFEv.s: Assembler messages:
/tmp/ccBWbFEv.s:447: Error: suffix or operands invalid for `nop'
make: *** [features.o] Error 1

# as --version
GNU assembler 2.15.92.0.2 20040927
Copyright 2002 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License.  This program has absolutely no warranty.
This assembler was configured for a target of `i386-redhat-linux'.

So maybe you could hardcode "nopl   (%eax)" ?

1 files changed, 1 insertions, 1 deletions

diff --git a/features.c b/features.c
index b7f39c1..c02cf86 100644
--- a/features.c
+++ b/features.c
@@ -469,7 +469,7 @@ static void test_longnop(void)
 	died = sigsetjmp(out, 1);
 
 	if (!died)
-		asm volatile("nopl 0(%eax)");
+		asm volatile(".byte 0x0f,0x1f,0x00 /* nopl 0(%eax) */");
 
 	printf("Long NOPs supported: %s\n", died ? "no" : "yes");
 }