[Bug go/66904] cmd/go: "#cgo pkg-config:" comments do not work with gccgo

[ian at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66904

--- Comment #1 from ian at gcc dot gnu.org <ian at gcc dot gnu.org> ---
Author: ian
Date: Wed Feb 10 18:30:27 2016
New Revision: 233290

URL: https://gcc.gnu.org/viewcvs?rev=233290&root=gcc&view=rev
Log:
        PR go/66904
    cmd/go: fix "#cgo pkg-config:" comments with gccgo

    Copy of https://golang.org/cl/18790 by Michael Hudson-Doyle.

    The unique difficulty of #cgo pkg-config is that the linker flags are
recorded
    when the package is compiled but (obviously) must be used when the package
is
    linked into an executable -- so the flags need to be stored on disk
somewhere.
    As it happens cgo already writes out a _cgo_flags file: nothing uses it
    currently, but this change adds it to the lib$pkg.a file when compiling a
    package, reads it out when linking (and passes a version of the .a file
with
    _cgo_flags stripped out of it to the linker). It's all fairly ugly but it
works
    and I can't really think of any way of reducing the essential level of
    ugliness.

    Update golang/go#11739.
    GCC PR 66904.

    Reviewed-on: https://go-review.googlesource.com/19431

Modified:
    trunk/gcc/go/gofrontend/MERGE
    trunk/libgo/go/cmd/go/build.go