[GCC]: Pass extra flags to gcc build.

There is no way to pass extra flags to gcc though
riscv-gnu-toolchain Makefile.

This is neccesary for me, because I has to rewrite gmp,
isl, mpfr, mpc folders in source of gcc project. Moreover,
I don't want to rebuild them with gcc.

Also I think, the opportunity to pass extra flags will be
convenient for many development purposes.

Author: mag-mga

Makefile.in

@@ -413,6 +413,7 @@ stamps/build-gcc-linux-stage1: $(GCC_SRCDIR) $(GCC_SRC_GIT) stamps/build-binutil
 		$(WITH_ARCH) \
 		$(WITH_TUNE) \
 		$(WITH_ISA_SPEC) \
+		$(GCC_EXTRA_CONFIGURE_FLAGS) \
 		CFLAGS_FOR_TARGET="-O2 $(CFLAGS_FOR_TARGET)" \
 		CXXFLAGS_FOR_TARGET="-O2 $(CXXFLAGS_FOR_TARGET)"
 	$(MAKE) -C $(notdir $@) inhibit-libc=true all-gcc
@@ -448,6 +449,7 @@ stamps/build-gcc-linux-stage2: $(GCC_SRCDIR) $(GCC_SRC_GIT) $(addprefix stamps/b
 		$(WITH_ARCH) \
 		$(WITH_TUNE) \
 		$(WITH_ISA_SPEC) \
+		$(GCC_EXTRA_CONFIGURE_FLAGS) \
 		CFLAGS_FOR_TARGET="-O2 $(CFLAGS_FOR_TARGET)" \
 		CXXFLAGS_FOR_TARGET="-O2 $(CXXFLAGS_FOR_TARGET)"
 	$(MAKE) -C $(notdir $@)
@@ -502,6 +504,7 @@ stamps/build-gcc-linux-native: $(GCC_SRCDIR) $(GCC_SRC_GIT) stamps/build-gcc-lin
 		$(WITH_ARCH) \
 		$(WITH_TUNE) \
 		$(WITH_ISA_SPEC) \
+		$(GCC_EXTRA_CONFIGURE_FLAGS) \
 	$(MAKE) -C $(notdir $@)
 	$(MAKE) -C $(notdir $@) install
 	cp -a $(INSTALL_DIR)/$(LINUX_TUPLE)/lib* $(SYSROOT)
@@ -580,6 +583,7 @@ stamps/build-gcc-newlib-stage1: $(GCC_SRCDIR) $(GCC_SRC_GIT) stamps/build-binuti
 		$(WITH_ARCH) \
 		$(WITH_TUNE) \
 		$(WITH_ISA_SPEC) \
+		$(GCC_EXTRA_CONFIGURE_FLAGS) \
 		CFLAGS_FOR_TARGET="-Os $(CFLAGS_FOR_TARGET)" \
 		CXXFLAGS_FOR_TARGET="-Os $(CXXFLAGS_FOR_TARGET)"
 	$(MAKE) -C $(notdir $@) all-gcc
@@ -680,6 +684,7 @@ stamps/build-gcc-newlib-stage2: $(GCC_SRCDIR) $(GCC_SRC_GIT) stamps/build-newlib
 		$(WITH_ARCH) \
 		$(WITH_TUNE) \
 		$(WITH_ISA_SPEC) \
+		$(GCC_EXTRA_CONFIGURE_FLAGS) \
 		CFLAGS_FOR_TARGET="-Os $(CFLAGS_FOR_TARGET)" \
 		CXXFLAGS_FOR_TARGET="-Os $(CXXFLAGS_FOR_TARGET)"
 	$(MAKE) -C $(notdir $@)
@@ -742,6 +747,7 @@ stamps/build-gcc-musl-stage1: $(GCC_SRCDIR) $(GCC_SRC_GIT) stamps/build-binutils
 		$(WITH_ARCH) \
 		$(WITH_TUNE) \
 		$(WITH_ISA_SPEC) \
+		$(GCC_EXTRA_CONFIGURE_FLAGS) \
 		CFLAGS_FOR_TARGET="-O2 $(CFLAGS_FOR_TARGET)" \
 		CXXFLAGS_FOR_TARGET="-O2 $(CXXFLAGS_FOR_TARGET)"
 	$(MAKE) -C $(notdir $@) inhibit-libc=true all-gcc
@@ -810,6 +816,7 @@ stamps/build-gcc-musl-stage2: $(GCC_SRCDIR) $(GCC_SRC_GIT) stamps/build-musl-lin
 		$(WITH_ARCH) \
 		$(WITH_TUNE) \
 		$(WITH_ISA_SPEC) \
+		$(GCC_EXTRA_CONFIGURE_FLAGS) \
 		CFLAGS_FOR_TARGET="-O2 $(CFLAGS_FOR_TARGET)" \
 		CXXFLAGS_FOR_TARGET="-O2 $(CXXFLAGS_FOR_TARGET)"
 	$(MAKE) -C $(notdir $@)

README.md

@@ -137,6 +137,9 @@ devtoolset-7 works.
 There are a number of additional options that may be passed to
 configure.  See './configure --help' for more details.
 
+Also you can define extra flags to pass to specific projects: ```BINUTILS_NATIVE_FLAGS_EXTRA, BINUTILS_TARGET_FLAGS_EXTRA, GCC_EXTRA_CONFIGURE_FLAGS, GDB_NATIVE_FLAGS_EXTRA, GDB_TARGET_FLAGS_EXTRA, GLIBC_NATIVE_FLAGS_EXTRA, GLIBC_TARGET_FLAGS_EXTRA```.
+Example: ```GCC_EXTRA_CONFIGURE_FLAGS=--with-gmp=/opt/gmp make linux```
+
 #### Set default ISA spec version
 
 `--with-isa-spec=` can specify the default version of the RISC-V Unprivileged