Support setting build parallelism, part 2

This extends usage of the "nproc" mechanism to all remaining parts and adds
 another "makeflags" variable to prevent too much logic from being scattered
 throughout the Makefile.  This variable could also be used to pass arbitrary
 flags to `make`.

For the sake of simplicity, we assume for now that Ninja understands all flags
 that GNU Make does.  If we ever need flags that only one of the two supports,
 we would have to add another "ninjaflags" variable.

Signed-Off-By: Dennis Schridde <devurandom@gmx.net>

Author: devurandom

Makefile

@@ -3,6 +3,7 @@ build_dir          := $(root_dir)/build
 sysroot_dir        := $(root_dir)/toolchain
 target             := riscv32-unknown-elf
 nproc              :=
+makeflags          := $(if $(nproc),-j$(nproc))
 ccache             := $(shell which ccache)
 
 
@@ -40,7 +41,7 @@ llvm-configure: $(llvm_src)
 $(llvm_build): llvm-configure
 
 llvm-build: $(llvm_build)
-	cmake --build $(llvm_build) -- $(if $(nproc),-j$(nproc))
+	cmake --build $(llvm_build) -- $(makeflags)
 $(llvm_build)/bin/llc: llvm-build
 
 llvm-install: $(llvm_build)/bin/llc
@@ -82,7 +83,7 @@ rust-build: $(sysroot_dir)/bin/cc
               --llvm-root=$(llvm_dest) \
               --enable-llvm-link-shared \
 		--enable-ccache
-	cd $(rust_src) && make
+	cd $(rust_src) && make $(makeflags)
 	cd $(rust_src) && make install
 $(rust_dest)/bin/rustc: rust-build
 rust: $(rust_dest)/bin/rustc
@@ -114,7 +115,7 @@ openocd-build: $(openocd_src)
     --enable-ftdi \
 		$(if $(ccache),CC="$(ccache) $(CC)") \
 		$(if $(ccache),CXX="$(ccache) $(CXX)")
-	$(MAKE) -C $(openocd_build)
+	$(MAKE) -C $(openocd_build) $(makeflags)
 	$(MAKE) -C $(openocd_build) install
 $(openocd_dest)/bin/openocd: openocd-build
 openocd: $(openocd_dest)/bin/openocd
@@ -136,7 +137,7 @@ binutils-build: $(binutils_src)
 		--enable-python \
 		$(if $(ccache),CC="$(ccache) $(CC)") \
 		$(if $(ccache),CXX="$(ccache) $(CXX)")
-	$(MAKE) -C $(binutils_build)
+	$(MAKE) -C $(binutils_build) $(makeflags)
 	$(MAKE) -C $(binutils_build) install
 $(binutils_dest)/bin/$(target)-gdb: binutils-build
 binutils: $(binutils_dest)/bin/$(target)-gdb