Add nsprenv.mk.in. This is a autoconf template for an nspr environment

nsprenv.mk

export USE_PTHREADS=@MOZ_NSPRENV_USE_PTHREADS@

export BUILD_OPT=@MOZ_NSPRENV_BUILD_OPT@

export NS_USE_GCC=@MOZ_NSPRENV_NS_USE_GCC@

export NO_MDUPDATE=@MOZ_NSPRENV_NO_MDUPDATE@

export NS_USE_NATIVE=@MOZ_NSPRENV_NS_USE_NATIVE@

export MOZILLA_CLIENT=@MOZ_NSPRENV_MOZILLA_CLIENT@