build system: allow building with w64devkit

Make some adjustments to the build system to allow busybox-w32
to be built with w64devkit:

- Strip drive prefix from CURDIR in Makefile to avoid confusing
  make with colons.

- Limit file redirection to a subshell in the usage_compressed and
  embedded_scripts scripts.  Otherwise it isn't possible to move
  the open generated file on Windows.

- Change the option tests in Kbuild.include to allow for /dev/null
  not existing on Windows.

- Create host binaries without a '.exe' extension.  Otherwise they're
  rebuilt more often than necessary.

- Modify split-include.c to allow for Windows' popen() not expanding
  wildcards.

(GitHub issue rmyorston#239)

Makefile

@@ -4,6 +4,10 @@ SUBLEVEL = 0
 EXTRAVERSION = .git
 NAME = Unnamed
 
+# Colon is used as a separator in makefiles.  Strip any drive prefix
+# from the current directory to avoid confusion.
+CURDIR := $(lastword $(subst :, ,$(CURDIR)))
+
 # *DOCUMENTATION*
 # To see a list of typical targets execute "make help"
 # More info can be located in ./README

applets/usage_compressed

@@ -16,6 +16,7 @@ if test $? != 0; then
 	exit 1
 fi
 
+(
 exec >"$target.$$"
 
 echo '#define UNPACKED_USAGE "" \'
@@ -58,5 +59,6 @@ echo '#define PACKED_USAGE \'
 	-e 's/\(...\)/0\1,/g' \
 	-e 's/$/ \\/'
 echo ''
+)
 
 mv -- "$target.$$" "$target"

scripts/Kbuild.include

@@ -52,25 +52,25 @@ endef
 # as-option
 # Usage: cflags-y += $(call as-option, -Wa$(comma)-isa=foo,)
 
-as-option = $(shell if $(CC) $(CFLAGS) $(1) -Wa,-Z -c -o /dev/null \
-	     -xassembler /dev/null > /dev/null 2>&1; then echo "$(1)"; \
+as-option = $(shell if $(CC) $(CFLAGS) $(1) -Wa,-Z -c -o - \
+	     -xassembler - </dev/null > /dev/null 2>&1; then echo "$(1)"; \
 	     else echo "$(2)"; fi ;)
 
 # cc-option
 # Usage: cflags-y += $(call cc-option, -march=winchip-c6, -march=i586)
 
-cc-option = $(shell if $(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null \
+cc-option = $(shell if $(CC) $(CFLAGS) $(1) -S -o - -xc - </dev/null \
              > /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi ;)
 
 # hostcc-option
 # Usage: hostcflags-y += $(call hostcc-option, -march=winchip-c6, -march=i586)
 
-hostcc-option = $(shell if $(HOSTCC) $(HOSTCFLAGS) $(1) -S -o /dev/null -xc /dev/null \
+hostcc-option = $(shell if $(HOSTCC) $(HOSTCFLAGS) $(1) -S -o - -xc - </dev/null \
              > /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi ;)
 
 # cc-option-yn
 # Usage: flag := $(call cc-option-yn, -march=winchip-c6)
-cc-option-yn = $(shell if $(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null \
+cc-option-yn = $(shell if $(CC) $(CFLAGS) $(1) -S -o - -xc - </dev/null \
                 > /dev/null 2>&1; then echo "y"; else echo "n"; fi;)
 
 # cc-option-align

scripts/Makefile.host

@@ -92,21 +92,38 @@ endif
 hostc_flags    = -Wp,-MD,$(depfile) $(__hostc_flags)
 hostcxx_flags  = -Wp,-MD,$(depfile) $(__hostcxx_flags)
 
+# Programs built for use on the host are defined without a suffix
+# (usually '.exe' on Windows).  Rather than adjust all the makefiles
+# force a suffix of '.' if the host platform is mingw32.  This will
+# result in binaries with no suffix.
+#
+# It's not a big deal if this doesn't work.  MSYS2 doesn't need it
+# and the downside is just that the programs will be rebuilt more
+# often than really needed.
+#
+host_target := $(shell $(HOSTCC) -v 2>&1 | grep ^Target:)
+host_platform := $(lastword $(subst -, ,$(host_target)))
+ifeq ($(host_platform),mingw32)
+dot := .
+else
+dot :=
+endif
+
 #####
 # Compile programs on the host
 
 # Create executable from a single .c file
 # host-csingle -> Executable
 quiet_cmd_host-csingle 	= HOSTCC  $@
-      cmd_host-csingle	= $(HOSTCC) $(hostc_flags) -o $@ $< \
+      cmd_host-csingle	= $(HOSTCC) $(hostc_flags) -o $@$(dot) $< \
 			  $(HOST_LOADLIBES) $(HOSTLOADLIBES_$(@F))
 $(host-csingle): %: %.c FORCE
 	$(call if_changed_dep,host-csingle)
 
 # Link an executable based on list of .o files, all plain c
 # host-cmulti -> executable
 quiet_cmd_host-cmulti	= HOSTLD  $@
-      cmd_host-cmulti	= $(HOSTCC) $(HOSTLDFLAGS) -o $@ \
+      cmd_host-cmulti	= $(HOSTCC) $(HOSTLDFLAGS) -o $@$(dot) \
 			  $(addprefix $(obj)/,$($(@F)-objs)) \
 			  $(HOST_LOADLIBES) $(HOSTLOADLIBES_$(@F))
 $(host-cmulti): %: $(host-cobjs) $(host-cshlib) FORCE

scripts/basic/split-include.c

@@ -197,13 +197,21 @@ int main(int argc, const char * argv [])
      * So by having an initial \n, strstr will find exact matches.
      */
 
+#ifdef __MINGW32__
+    fp_find = popen("find . -type f -name \"*.h\" -print", "r");
+#else
     fp_find = popen("find * -type f -name \"*.h\" -print", "r");
+#endif
     if (fp_find == 0)
 	ERROR_EXIT( "find" );
 
     line[0] = '\n';
     while (fgets(line+1, buffer_size, fp_find))
     {
+#ifdef __MINGW32__
+	line[2] = '\n';
+# define line (line + 2)
+#endif
 	if (strstr(list_target, line) == NULL)
 	{
 	    /*
@@ -226,6 +234,9 @@ int main(int argc, const char * argv [])
 		    ERROR_EXIT(line);
 	    }
 	}
+#ifdef __MINGW32__
+# undef line
+#endif
     }
 
     if (pclose(fp_find) != 0)

scripts/embedded_scripts

@@ -90,6 +90,7 @@ concatenate_scripts() {
 	done
 }
 
+(
 exec >"$target.$$"
 
 if [ $n -ne 0 ]
@@ -127,5 +128,6 @@ then
 		-e 's/$/ \\/'
 	printf '\n'
 fi
+)
 
 mv -- "$target.$$" "$target"