linux-perf: Fix BPF feature detection

debian/changelog

@@ -1,3 +1,9 @@
+linux (4.18.10-3) UNRELEASED; urgency=medium
+
+  * linux-perf: Fix BPF feature detection
+
+ -- Ben Hutchings <ben@decadent.org.uk>  Mon, 08 Oct 2018 19:02:53 +0100
+
 linux (4.18.10-2) unstable; urgency=medium
 
   [ Ben Hutchings ]

debian/patches/bugfix/all/tools-build-remove-bpf-run-time-check-at-build-time.patch

@@ -11,14 +11,17 @@ Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
 ---
 --- a/tools/build/feature/test-bpf.c
 +++ b/tools/build/feature/test-bpf.c
-@@ -31,9 +31,5 @@ int main(void)
- 	attr.kern_version = 0;
+@@ -35,8 +35,10 @@ int main(void)
  	attr.prog_flags = 0;
  
--	/*
+ 	/*
 -	 * Test existence of __NR_bpf and BPF_PROG_LOAD.
 -	 * This call should fail if we run the testcase.
--	 */
++	 * bwh: Don't use the bpf() syscall as we might be building on a
++	 * much older kernel.  Do "use" the attr structure here to avoid
++	 * a "set but not used" warning.
+ 	 */
 -	return syscall(__NR_bpf, BPF_PROG_LOAD, &attr, sizeof(attr));
++	(void)&attr;
 +	return 0;
  }