Make cross-compiling for Windows a little bit easier

Makefile

@@ -36,17 +36,18 @@ NGS_VER ?= 2.10.2
 VDB_VER ?= 2.10.2
 
 # Detect Cygwin or MinGW
-WINDOWS :=
-MINGW :=
 ifneq (,$(findstring mingw,$(shell $(CXX) --version)))
   WINDOWS := 1
   MINGW := 1
+endif
 
-  CXX ?= x86_64-w64-mingw32-g++-posix
-  CC  ?= x86_64-w64-mingw32-gcc-posix
-  AR  ?= x86_64-w64-mingw32-ar
-  RC  ?= x86_64-w64-mingw32-windres
-  STRIP ?= x86_64-w64-mingw32-strip
+ifeq (1, $(MINGW))
+  CXX = x86_64-w64-mingw32-g++-posix
+  CC  = x86_64-w64-mingw32-gcc-posix
+  AR  = x86_64-w64-mingw32-ar
+  RC  = x86_64-w64-mingw32-windres
+  LD  = x86_64-w64-mingw32-ld
+  STRIP = x86_64-w64-mingw32-strip
 endif
 
 # POSIX memory-mapped files not currently supported on Windows
@@ -550,7 +551,6 @@ perl-deps:
 	eval `perl -I $(CURDIR)/.tmp/lib/perl5 -Mlocal::lib=$(CURDIR)/.tmp` ; \
 	$(CURDIR)/.tmp/bin/cpanm --force File::Which Math::Random Clone Test::Deep Sys::Info ; \
 
-#make -f win32/Makefile.gcc CC=x86_64-w64-mingw32-gcc-posix AR=x86_64-w64-mingw32-ar RC=x86_64-w64-mingw32-windres STRIP=x86_64-w64-mingw32-strip
 .PHONY: static-libs
 static-libs:
 	if [ ! -d "$(CURDIR)/.tmp" ] ; then \
@@ -564,14 +564,14 @@ static-libs:
 	DL=$$( ( which wget >/dev/null 2>&1 && echo "wget --no-check-certificate" ) || echo "curl -LOk") ; \
 	if [ ! -f "$(CURDIR)/.tmp/lib/libz.a" ] ; then \
 		$$DL http://zlib.net/zlib-1.3.tar.gz && tar xzf zlib-1.3.tar.gz && cd zlib-1.3 ; \
-		$(if $(MINGW), $(MAKE) -f win32/Makefile.gcc, ./configure --static && make) && \
+		$(if $(MINGW), $(MAKE) libz.a -f win32/Makefile.gcc CC=$(CC) AR=$(AR) RC=$(RC) STRIP=$(STRIP) LD=$(LD), ./configure --static && make) && \
 		cp zlib.h zconf.h $(CURDIR)/.tmp/include && cp libz.a $(CURDIR)/.tmp/lib ; \
 		rm -rf zlib-1.3* ; \
 	fi ; \
         if [ ! -f "$(CURDIR)/.tmp/lib/libzstd.a" ]; then \
                 cd $(CURDIR)/.tmp ; \
                 $$DL https://github.com/facebook/zstd/releases/download/v1.5.5/zstd-1.5.5.tar.gz && tar xzf zstd-1.5.5.tar.gz ; \
-                cd zstd-1.5.5 && $(MAKE) lib ; \
+                cd zstd-1.5.5 && $(MAKE) CC=$(CC) AR=$(AR) RC=$(RC) STRIP=$(STRIP) LD=$(LD) lib ; \
                 cd $(CURDIR)/.tmp/zstd-1.5.5/lib && cp zstd.h $(CURDIR)/.tmp/include && cp libzstd.a $(CURDIR)/.tmp/lib ; \
 		rm -rf zstd-1.5.5* ; \
         fi