fullcircle: Check that we found the CFLAGS

So that we don't try to compile something that wasn't built with a
CFLAGS or even gcc, like .o made from ASM files.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
diff --git a/fullcircle b/fullcircle
index a5ef4cc..92fa573 100755
--- a/fullcircle
+++ b/fullcircle
@@ -31,6 +31,9 @@
 
 CFLAGS=$(readelf -wi $file | grep -w DW_AT_producer | sed -r      's/.*\)( -[[:alnum:]]+.*)+/\1/g')
 
+# Check if we managed to do the sed or if this is something like GNU AS
+[ "${CFLAGS/DW_AT_producer/}" != "${CFLAGS}" ] && exit
+
 ${pfunct_bin} --compile $file > $c_output
 gcc $CFLAGS -c -g $c_output -o $o_output
 ${codiff_bin} -q -s $file $o_output