go: runtime: TestGcSys fails on linux/amd64

What version of Go are you using (go version)?

$ go version
go version devel +1645dfa23f Fri Nov 2 23:22:57 2018 +0000 linux/amd64

Does this issue reproduce with the latest release?

It reproduces at master.

What operating system and processor architecture are you using (go env)?

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/tom/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/tom/go"
GOPROXY=""
GORACE=""
GOROOT="/home/tom/go/dev-go"
GOTMPDIR=""
GOTOOLDIR="/home/tom/go/dev-go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build842792331=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Tried to build go at master with ./all.bash.

What did you expect to see?

Test passing with:

ok  	runtime XX.XXXs

What did you see instead?

Test failed with:

--- FAIL: TestGcSys (0.05s)
    gc_test.go:33: expected "OK\n", but got "using too much memory: 70877184 bytes\n"
FAIL
FAIL	runtime	18.959s

This is the same issue as #27636 and #27156, but for linux/amd64 under Fedora 29.