This change:
* Uses the installed version of both the library and the pkgconfig file,
which fixes path resolution on Ubuntu Xenial.
* Uses quoting liberally so that paths with spaces in them are correctly
handled.
* Moves the build+install directories to static-build/ in the git2go
repository to avoid having a dirty vendor/libgit2 checkout.
When using the static linking option on platforms that use pkg-config,
use ONLY pkg-config to get the CFLAGS and LDFLAGS. This prevents pulling
in dependencies and flags for any non-vendored version that may be
present on the host.
The main practical effect of this is that if someone doesn't need/want
any sort of remote access support at all they can completely disable
libcurl, libssh2, libssl, etc and produce a smaller/simpler binary and
greatly simplify their build-time dependencies. When done properly, the
generated pkg-config file will tell cgo everything it needs to know.
This also prevents confusion if there is a system copy of libgit2 that
is being given priority over the vendored build.
Signed-off-by: Ryan Graham <r.m.graham@gmail.com>