libbpf: Ignore warnings about "inefficient alignment"

Some consumers of libbpf compile the code base with different warnings
enabled. In a report for perf, for example, -Wpacked was set which
caused warnings about "inefficient alignment" to be emitted on a subset
of supported architectures.

With this change we silence specifically those warnings, as we intentionally
worked with packed structs.

This is a similar resolution as in b2f10cd4e805 ("perf cpumap: Fix alignment
for masks in event encoding").

Fixes: 1eebcb60633f ("libbpf: Implement basic zip archive parsing support")
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Signed-off-by: Daniel Müller <deso@posteo.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/bpf/CA+G9fYtBnwxAWXi2+GyNByApxnf_DtP1-6+_zOKAdJKnJBexjg@mail.gmail.com/
Link: https://lore.kernel.org/bpf/20230315171550.1551603-1-deso@posteo.net

src/zip.c

@@ -16,6 +16,10 @@
 #include "libbpf_internal.h"
 #include "zip.h"
 
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wpacked"
+#pragma GCC diagnostic ignored "-Wattributes"
+
 /* Specification of ZIP file format can be found here:
  * https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXT
  * For a high level overview of the structure of a ZIP file see
@@ -119,6 +123,8 @@ struct local_file_header {
 	__u16 extra_field_length;
 } __attribute__((packed));
 
+#pragma GCC diagnostic pop
+
 struct zip_archive {
 	void *data;
 	__u32 size;