Add pkg-config support to flashmap

This adds a rule to the Makefile to generate a pkg-config .pc file
and install it if:
1) /usr/lib/pkgconfig is a directory
2) The user sets an environment variable.

The latter is useful for sandboxed environments since /usr/lib/pkgconfig
might exist in the target environment but not the sandbox where flashmap
is being built.

BUG=none
TEST=Test compiled on Goobuntu, cros_sdk (emerge), and x86-generic (emerge-x86-generic)

Change-Id: Id45ef5300b693f8258671729b624b82ea1780965
1 file changed