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
From-SVN: r233290
931f434a72