build: use $(MAKE) to represent make executable

Prior to this commit, our Makefiles assumed the name of the make program
was simply "make".

Since we use GNU make extensions, this isn't always the case --
operating systems like FreeBSD come with their own implementation named
make which can be incompatible with the extensions used in by tinygo.

To run a compatible make on some of these systems, we have explicitly
call GNU make by running gmake.

This commit changes references to the command "make" to "$(MAKE)" which
is a variable that contains the name of the executable invoked to
process the Makefile.

This allow the Makefiles to be uniformly processed by the same make
program.

Makefile

@@ -265,7 +265,7 @@ endif
 wasi-libc: lib/wasi-libc/sysroot/lib/wasm32-wasi/libc.a
 lib/wasi-libc/sysroot/lib/wasm32-wasi/libc.a:
 	@if [ ! -e lib/wasi-libc/Makefile ]; then echo "Submodules have not been downloaded. Please download them using:\n  git submodule update --init"; exit 1; fi
-	cd lib/wasi-libc && make -j4 EXTRA_CFLAGS="-O2 -g -DNDEBUG -mnontrapping-fptoint -msign-ext" MALLOC_IMPL=none CC=$(CLANG) AR=$(LLVM_AR) NM=$(LLVM_NM)
+	cd lib/wasi-libc && $(MAKE) -j4 EXTRA_CFLAGS="-O2 -g -DNDEBUG -mnontrapping-fptoint -msign-ext" MALLOC_IMPL=none CC=$(CLANG) AR=$(LLVM_AR) NM=$(LLVM_NM)
 
 # Check for Node.js used during WASM tests.
 NODEJS_VERSION := $(word 1,$(subst ., ,$(shell node -v | cut -c 2-)))
@@ -280,7 +280,7 @@ endif
 
 # Build the Go compiler.
 tinygo:
-	@if [ ! -f "$(LLVM_BUILDDIR)/bin/llvm-config" ]; then echo "Fetch and build LLVM first by running:"; echo "  make llvm-source"; echo "  make $(LLVM_BUILDDIR)"; exit 1; fi
+	@if [ ! -f "$(LLVM_BUILDDIR)/bin/llvm-config" ]; then echo "Fetch and build LLVM first by running:"; echo "  $(MAKE) llvm-source"; echo "  $(MAKE) $(LLVM_BUILDDIR)"; exit 1; fi
 	CGO_CPPFLAGS="$(CGO_CPPFLAGS)" CGO_CXXFLAGS="$(CGO_CXXFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" $(GOENVFLAGS) $(GO) build -buildmode exe -o build/tinygo$(EXE) -tags "byollvm osusergo" -ldflags="-X github.com/tinygo-org/tinygo/goenv.GitSha1=`git rev-parse --short HEAD`" .
 test: wasi-libc check-nodejs-version
 	CGO_CPPFLAGS="$(CGO_CPPFLAGS)" CGO_CXXFLAGS="$(CGO_CXXFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" $(GO) test $(GOTESTFLAGS) -timeout=20m -buildmode exe -tags "byollvm osusergo" ./builder ./cgo ./compileopts ./compiler ./interp ./transform .

docs/Makefile

@@ -16,7 +16,7 @@ I18NSPHINXOPTS  = $(PAPEROPT_$(PAPER)) $(SPHINXOPTS) .
 
 .PHONY: help
 help:
-	@echo "Please use \`make <target>' where <target> is one of"
+	@echo "Please use \`$(MAKE) <target>' where <target> is one of"
 	@echo "  html       to make standalone HTML files"
 	@echo "  dirhtml    to make HTML files named index.html in directories"
 	@echo "  singlehtml to make a single large HTML file"