hg: build-infra/jdk9: Fixed BUILD_TOOLCHAIN to handle SYSROOT flags better

[ingemar.aberg at oracle.com]

Changeset: 1e4f41790070
Author:    iaberg
Date:      2015-06-01 11:04 +0200
URL:       http://hg.openjdk.java.net/build-infra/jdk9/rev/1e4f41790070

Fixed BUILD_TOOLCHAIN to handle SYSROOT flags better

! common/autoconf/generated-configure.sh
! common/autoconf/spec.gmk.in
! common/autoconf/toolchain.m4
! make/common/NativeCompilation.gmk