configure.ac: Add --enable-build-with-cxx.

configure.ac: Add --enable-build-with-cxx.

./:	* configure.ac: Add --enable-build-with-cxx.  When set, add c++ to
	boot_languages.  Only bootstrap target libraries listed in
	target_libs for some boot language.  Add --with-stage1-ldflags,
	--with-stage1-libs, --with-boot-ldflags, --with-boot-libs.  Remove
	with_host_libstdcxx from ppllibs.  Only add -fkeep-inline-functions
	if not building with C++.
	* Makefile.def: For target_module libstdc++-v3, set bootstrap=true.
	* Makefile.tpl (STAGE1_LDFLAGS, STAGE1_LIBS): New variables.
	(POSTSTAGE1_LDFLAGS, POSTSTAGE1_LIBS): New variables.
	(HOST_EXPORTS): Add STAGE1_LDFLAGS to LDFLAGS.  Export HOST_LIBS.
	(POSTSTAGE1_HOST_EXPORTS): Set CXX and CXX_FOR_BUILD.  Add
	POSTSTAGE1_LDFLAGS to LDFLAGS.  Export HOST_LIBS.
	(POSTSTAGE1_FLAGS_TO_PASS): Likewise.
	* configure, Makefile.in: Rebuild.
gcc/:
	* configure.ac: Invoke AC_PROG_CXX.  Separate C specific warnings
	from loose_warn into c_loose_warn and from strict_warn into
	c_strict_warn.  Set and substitute warn_cxxflags.  Check for
	--enable-build-with-cxx.  Set and substitute
	ENABLE_BUILD_WITH_CXX.  Set and substitute HOST_LIBS.
	* Makefile.in (CXXFLAGS): New variable.
	(C_LOOSE_WARN, C_STRICT_WARN): New variables.
	(GCC_WARN_CFLAGS): Add $(C_LOOSE_WARN).  Add $(C_STRICT_WARN) if
	the default is the same as $(STRICT_WARN).
	(GCC_WARN_CXXFLAGS, WARN_CXXFLAGS): New variables.
	(CXX): New variable.
	(COMPILER): New value if ENABLE_BUILD_WITH_CXX.
	(COMPILER_FLAGS, LINKER, LINKER_FLAGS): Likewise.
	(ALL_COMPILERFLAGS, ALL_LINKERFLAGS): Likewise.
	(HOST_LIBS): New variable.
	(GCC_CFLAGS): Add $(C_LOOSE_WARN).
	(ALL_CXXFLAGS): New variable.
	(LIBS, BACKENDLIBS): Add $(HOST_LIBS).
	* doc/install.texi (Configuration): Document
	--enable-build-with-cxx, --with-stage1-ldflags,
	--with-stage1-libs, --with-boot-ldflags, --with-boot-libs.
	* configure: Rebuild.

From-SVN: r148889