Allow building using native GNU make

Avoid the use of sed when building Compat.ml and use the NUL device.

.gitattributes

@@ -2,3 +2,4 @@
 
 msvs-detect text eol=lf
 checkenv text eol=lf
+Compat.cmd text eol=crlf

Compat.cmd

@@ -0,0 +1,29 @@
+@setlocal
+@echo off
+
+:: This can be done as (slightly long) one-liner, but embedded in Makefile it
+:: encodes the knowledge that GNU make uses batch files internally, which is a
+:: bit brittle. findstr /N is a trick to allow blank lines to be included. More
+:: subtly, it allows tagged blank lines to be detected.
+for /f "tokens=1* delims=:" %%a in ('findstr /N /R "^" %2') do (
+  rem Handle blank lines in the file
+  if "%%b" equ "" (
+    echo.
+  ) else (
+    for /f "tokens=1* delims=@" %%l in ("%%b") do (
+      rem If %%l == %%b then the line didn't contain @ - we already know the
+      rem line isn't blank.
+      if "%%l" equ "%%b" (
+        echo %%l
+      ) else (
+        if %1 lss %%l00 (
+          if "%%m" equ "" (
+            echo.
+          ) else (
+            echo %%m
+          )
+        )
+      )
+    )
+  )
+)

Makefile

@@ -8,12 +8,28 @@
 VERSION = 0.42
 all: flexlink.exe support
 
-OCAML_CONFIG_FILE=$(shell cygpath -ad "$(shell ocamlopt -where 2>/dev/null)/Makefile.config" 2>/dev/null)
+export override OCAML_DETECT_CMD = detect
+SHELL_IS_CMD := \
+  $(if $(filter %OCAML_DETECT_CMD%, $(shell echo %OCAML_DETECT_CMD%)),,true)
+unexport OCAML_DETECT_CMD
+undefine DETECT_WINDOWS_SHELL
+
+NULL_DEVICE := $(if $(SHELL_IS_CMD), NUL, /dev/null)
+
+ifeq ($(SHELL_IS_CMD),)
+RM_F = rm -f $(1)
+TOUCH = touch
+else
+RM_F = $(if $(wildcard $(1)),del /f $(subst /,\,$(wildcard ($1))))
+TOUCH = type NUL >
+endif
+
+OCAML_CONFIG_FILE=$(shell cygpath -ad "$(shell ocamlopt -where 2>$(NULL_DEVICE))/Makefile.config" 2>$(NULL_DEVICE))
 include $(OCAML_CONFIG_FILE)
 OCAMLOPT=ocamlopt
 EMPTY=
 SPACE=$(EMPTY) $(EMPTY)
-OCAML_VERSION:=$(firstword $(subst ~, ,$(subst +, ,$(shell $(OCAMLOPT) -version 2>/dev/null))))
+OCAML_VERSION:=$(firstword $(subst ~, ,$(subst +, ,$(shell $(OCAMLOPT) -version 2>$(NULL_DEVICE)))))
 ifeq ($(OCAML_VERSION),)
 OCAML_VERSION:=0
 COMPAT_VERSION:=0
@@ -148,8 +164,8 @@ build_mingw64: flexdll_mingw64.o flexdll_initer_mingw64.o
 OBJS = version.ml Compat.ml coff.ml cmdline.ml create_dll.ml reloc.ml
 
 COMPILER-$(COMPAT_VERSION):
-	rm -f COMPILER-*
-	touch COMPILER-$(COMPAT_VERSION)
+	$(call RM_F, COMPILER-*)
+	$(TOUCH) COMPILER-$(COMPAT_VERSION)
 
 test_ver = $(shell if [ $(COMPAT_VERSION) -ge $(1) ] ; then echo ge ; fi)
 
@@ -163,11 +179,15 @@ COMPAT_LEVEL = $(eval COMPAT_LEVEL := \
            $$(if $$(call test_ver,40700),407)))$(COMPAT_LEVEL)
 
 Compat.ml: Compat.ml.in COMPILER-$(COMPAT_VERSION)
+ifeq ($(SHELL_IS_CMD),)
 	sed -e '$(if $(COMPAT_LEVEL),/^$(subst $(SPACE),@\|^,$(COMPAT_LEVEL))@/d;)s/^[0-9]*@//' $< > $@
+else
+	Compat.cmd $(COMPAT_VERSION) $< > $@
+endif
 
 flexlink.exe: $(OBJS) $(RES)
 	@echo Building flexlink.exe with TOOLCHAIN=$(TOOLCHAIN) for OCaml $(OCAML_VERSION)
-	rm -f flexlink.exe
+	$(call RM_F, flexlink.exe)
 	$(RES_PREFIX) $(OCAMLOPT) -o flexlink.exe $(LINKFLAGS) $(OBJS)
 
 version.res: version.rc