runtime: use -buildmode=pie in testCgoPprofPIE  instead of -extldflags=-pie
runtime: use -buildmode=pie in testCgoPprofPIE  instead of -extldflags=-pie

Errors occur in runtime test testCgoPprofPIE when the test
is built by passing -pie to the external linker with code
that was not built as PIC. This occurs on ppc64le because
non-PIC is the default, and fails only on newer distros
where the address range used for programs is high enough
to cause relocation overflow. This test should be built
with -buildmode=pie since that correctly generates PIC
with -pie.

Related issues are #21954 and #22126.

Updates #22459

Change-Id: Ib641440bc9f94ad2b97efcda14a4b482647be8f7
Reviewed-on: https://go-review.googlesource.com/73970
Run-TryBot: Lynn Boger <b27445fe6fb259c37b8e0a4ce56e22e2413754bf@linux.vnet.ibm.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/go,cloudflare/go,golang/go,josharian/go,CAFxX/go,nawawi/go,CAFxX/go,CAFxX/go,codestation/go,cloudflare/go,akutz/go,codestation/go,CAFxX/go,codestation/go,nawawi/go,nawawi/go,cloudflare/go,nawawi/go,codestation/go,nawawi/go,josharian/go,Cofyc/go,josharian/go,akutz/go,nawawi/go,cloudflare/go,golang/go,josharian/go,golang/go,CAFxX/go,Cofyc/go,codestation/go,CAFxX/go,Cofyc/go,nawawi/go,akutz/go,akutz/go,akutz/go,golang/go,CAFxX/go,josharian/go,josharian/go,josharian/go,akutz/go,cloudflare/go,golang/go,akutz/go,akutz/go,cloudflare/go,Cofyc/go,nawawi/go,codestation/go,Cofyc/go,josharian/go,Cofyc/go,golang/go,codestation/go,cloudflare/go,golang/go,Cofyc/go,codestation/go,christopher-henderson/Go,cloudflare/go,CAFxX/go,Cofyc/go