cmd/link: link libgcc archive after mingw archives

When compiling with the race detector using modern mingw, this prevents:

    libgcc(.text): relocation target ___chkstk_ms not defined

Change-Id: I2095ad09a535505b54f9ff2d3075fd20ac85e515
Reviewed-on: https://go-review.googlesource.com/c/go/+/295910


Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>