Fix some compiler settings/paths for MinGW

It seems that you have to jump through hoops to make trivial things
such as "install.exe" do the right thing on Windows...

Also, it seems that Windows Vista deliberately broke "access()".
Apparently, they used that name in their runtime, but that function
does something completely different than POSIX access().  So define
__USE_MINGW_ACCESS to work around that.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Makefile

@@ -176,7 +176,7 @@ CC = gcc
 AR = ar
 RM = rm -f
 TAR = tar
-INSTALL = install
+INSTALL = /bin/install
 RPMBUILD = rpmbuild
 TCL_PATH = tclsh
 TCLTK_PATH = wish
@@ -373,7 +373,7 @@ BUILTIN_OBJS = \
 	builtin-pack-refs.o
 
 GITLIBS = $(LIB_FILE) $(XDIFF_LIB)
-EXTLIBS = -lz
+EXTLIBS = /mingw/lib/libz.a
 
 #
 # Platform specific tweaks
@@ -488,7 +488,7 @@ ifneq (,$(findstring MINGW,$(uname_S)))
 	NO_SYMLINKS=YesPlease
 	NO_SVN_TESTS=YesPlease
 	NO_PERL_MAKEMAKER=YesPlease
-	COMPAT_CFLAGS += -DNO_ETC_PASSWD -DNO_ST_BLOCKS -DSTRIP_EXTENSION=\".exe\" -I compat
+	COMPAT_CFLAGS += -DNO_ETC_PASSWD -DNO_ST_BLOCKS -DSTRIP_EXTENSION=\".exe\" -D__USE_MINGW_ACCESS -I compat
 	COMPAT_OBJS += compat/mingw.o compat/fnmatch.o compat/regex.o
 	EXTLIBS += -lws2_32
 	X = .exe