selftests/bpf: Override PKG_CONFIG for static builds

A library may need to depend on additional archive files for static
builds so pkg-config should be instructed to list them.

Signed-off-by: Akihiko Odaki <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: akihikodaki

tools/testing/selftests/bpf/README.rst

@@ -77,7 +77,7 @@ In case of linker errors when running selftests, try using static linking:
 
 .. code-block:: console
 
-  $ LDLIBS=-static vmtest.sh
+  $ LDLIBS=-static PKG_CONFIG='pkg-config --static' vmtest.sh
 
 .. note:: Some distros may not support static linking.