build: run cgo tests with -pie if the external linker supports it.

PIE binaries can be built by the Go compiler in external link mode with
extldflags="-pie". These binaries support ASLR (address space layout
randomization) when executed on systems with appropriate kernel/dynamic
linker support.

This CL enables some cgo tests to run with -pie as a sanity check (in
addition to the other linker flag combinations they already test).

I have tested this functionality more thoroughly by building the full
compiler testsuite (test/...) and standard library tests with -pie
and executing them remotely on ChromeOS devices for all three linux
architectures (linux_amd64, linux_386, and linux_arm).

Change-Id: I3f644a72e94c3341f3360dfee58db5ec3a591e26
Reviewed-on: https://go-review.googlesource.com/6280Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/run.bash

@@ -158,6 +158,13 @@ android-arm | dragonfly-386 | dragonfly-amd64 | freebsd-386 | freebsd-amd64 | fr
 			go test -ldflags '-linkmode=external' ../nocgo || exit 1
 			go test -ldflags '-linkmode=external -extldflags "-static -pthread"' ../nocgo || exit 1
 		fi
+		if ! $CC -xc -o /dev/null -pie - 2>/dev/null <<<'int main() {}' ; then
+			echo "No support for -pie found, skip cgo PIE test."
+		else
+			go test -ldflags '-linkmode=external -extldflags "-pie"' || exit 1
+			go test -ldflags '-linkmode=external -extldflags "-pie"' ../testtls || exit 1
+			go test -ldflags '-linkmode=external -extldflags "-pie"' ../nocgo || exit 1
+		fi
 		;;
 	esac
 	;;