ci: make sure to not override CFLAGS

Use EXTRA_CFLAGS instead of overriding CFLAGS.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

travis-ci/managers/test_compile.sh

@@ -1,7 +1,8 @@
 #!/bin/bash
 set -euox pipefail
 
-CFLAGS=${CFLAGS:-}
+EXTRA_CFLAGS=${EXTRA_CFLAGS:-}
+EXTRA_LDFLAGS=${EXTRA_LDFLAGS:-}
 
 cat << EOF > main.c
 #include <bpf/libbpf.h>
@@ -11,4 +12,4 @@ int main() {
 EOF
 
 # static linking
-${CC:-cc} ${CFLAGS} -o main -I./install/usr/include main.c ./build/libbpf.a -lelf -lz
+${CC:-cc} ${EXTRA_CFLAGS} ${EXTRA_LDFLAGS} -o main -I./include/uapi -I./install/usr/include main.c ./build/libbpf.a -lelf -lz