RUBY-29825 add a separate Makefile.cross for easier cross-compilation to other platforms.

By default, we cross-compile for `aarch64`, but that could be adjusted via `HOST` variable.

Also cleaned up the `Makefile` and updated README.

Reviewed-by: IJ-CR-102814

GitOrigin-RevId: b65519b2ab6a3461f0e621d5dcc832b083948fef

native/WslTools/.gitignore

@@ -1,5 +1,6 @@
 .idea
 musl
+musl-*/
 *.tgz
 *.tar.gz
 wslproxy

native/WslTools/Makefile

@@ -7,23 +7,23 @@ MUSL_HOME := $(HOME)/musl
 MUSL_CC := $(MUSL_HOME)/bin/musl-gcc
 
 CFLAGS = -Wall -Wextra -pedantic -Werror -Os -D_POSIX_SOURCE=1 -D_BSD_SOURCE=1
-LDLIBS = -static
+LDFLAGS = -static
 CC = $(MUSL_CC)
 
 all: $(MUSL_CC) wslproxy wslhash
 
-musl:
+$(MUSL_DISTR):
 	@echo I will now download musl. If it fails, check you have wget and see README
 	wget https://musl.libc.org/releases/musl-$(MUSL_VER).tar.gz -O musl.tar.gz
 	tar xfvz musl.tar.gz && mv musl-$(MUSL_VER) $(MUSL_DISTR)
 
-$(MUSL_CC): musl
+$(MUSL_CC): $(MUSL_DISTR)
 	cd $(MUSL_DISTR) && ./configure --prefix=$(MUSL_HOME) --syslibdir=$(MUSL_HOME)/lib && $(MAKE) && $(MAKE) install
 
-wslproxy: $(SOURCES) | $(MUSL_CC)
+wslproxy: wslproxy.c | $(MUSL_CC)
 wslhash: wslhash.c xxhash.h xxhash.c | $(MUSL_CC)
 
 .PHONY: all clean
 
 clean:
-	$(RM) wslproxy wslhash
+	$(RM) wslproxy wslhash

native/WslTools/Makefile.cross

@@ -0,0 +1,20 @@
+BUILD := $(shell uname -m)
+HOST := aarch64
+
+MUSL_CROSS_VER := 10
+MUSL_CROSS_DISTR := musl-$(HOST)
+MUSL_CROSS_CC := ./$(MUSL_CROSS_DISTR)/bin/$(HOST)-linux-musl-gcc
+
+all: $(MUSL_CROSS_DISTR) $(MUSL_CROSS_CC)
+	make CC="$(MUSL_CROSS_CC)" $(MAKECMDGOALS)
+
+$(MUSL_CROSS_DISTR):
+	@echo I will now download musl cross-compile toolchain. If it fails, check you have wget and see README
+	wget "https://more.musl.cc/$(MUSL_CROSS_VER)/$(BUILD)-linux-musl/$(HOST)-linux-musl-cross.tgz" -O "$(MUSL_CROSS_DISTR).tgz"
+	tar xfvz "$(MUSL_CROSS_DISTR).tgz"
+	mv "$(HOST)-linux-musl-cross" "$(MUSL_CROSS_DISTR)"
+
+.PHONY: all clean
+
+clean:
+	$(RM) wslproxy wslhash

native/WslTools/README.txt

@@ -30,4 +30,14 @@ Getting musl manually:
 See https://wiki.musl-libc.org/getting-started.html for more info
 
 Q: I got error opening project in CLion:
-A: Make sure you run "make". Then, tools->Makefile->Reload
+A: Make sure you run "make". Then, tools->Makefile->Reload
+
+Q: How do I compile binaries for aarch64 platform?
+A: Run "make -f Makefile.cross clean all". The required musl cross-compiler will be downloaded and
+ all tools will be cross-compiled for aarch64 platform.
+
+Q: How do I check the target platform of the compiled binary?
+A: Check the output of "file YOUR_BINARY".
+
+Q: How do I test that cross-compiled binary works on aarch64?
+A: Run "sudo apt install qemu-user-static" (adjust for your distro). Then run "qemu-aarch64-static YOUR_BINARY".