perf: tools: Fix cross building

perf: tools: Fix cross building

Currently the feature-checks Makefile does not inherit $(CC), and calls
cc rather than $(CROSS_COMPILE)gcc. Thus the feature checks invoke the
native toolchain rather than the cross toolchain, and can identify
features as available when they are not. This can break the build.

Additionally the native pkg-config is always called as opposed to
$(CROSS_COMPILE)pkg-config, so the wrong flags and paths may be passed
to the cross compiler.

This patch passes CROSS_COMPILE down to the feature-checks Makefile, and
forces its use. Additionally pkg-config is replaced with
$(CROSS_COMPILE)pkg-config via a new $(PKG_CONFIG) variable. This patch
has been build tested on x86_64 and arm.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/1389782648-4417-4-git-send-email-mark.rutland@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>