Allow the user to flip "--with-system-zlib"

We need this to have different polarity for different platforms (Windows
vs RedHat).  I don't know how to autodetect this for now, so I'm just
doing it manually.

Makefile.in

@@ -153,7 +153,7 @@ stamps/build-gcc-linux-stage1: $(srcdir)/riscv-gcc stamps/build-binutils-linux \
 		--without-headers \
 		--disable-shared \
 		--disable-threads \
-		--with-system-zlib \
+		@with_system_zlib@ \
 		--enable-tls \
 		--enable-languages=c \
 		--disable-libatomic \
@@ -182,7 +182,7 @@ stamps/build-gcc-linux-stage2: $(srcdir)/riscv-gcc $(addprefix stamps/build-glib
 		$(CONFIGURE_HOST) \
 		--prefix=$(INSTALL_DIR) \
 		--with-sysroot=$(SYSROOT) \
-		--with-system-zlib \
+		@with_system_zlib@ \
 		--enable-shared \
 		--enable-tls \
 		--enable-languages=c,c++,fortran \
@@ -223,7 +223,7 @@ stamps/build-gcc-newlib-stage1: $(srcdir)/riscv-gcc stamps/build-binutils-newlib
 		--disable-threads \
 		--disable-tls \
 		--enable-languages=c,c++ \
-		--with-system-zlib \
+		@with_system_zlib@ \
 		--with-newlib \
 		--disable-libmudflap \
 		--disable-libssp \
@@ -264,7 +264,7 @@ stamps/build-gcc-newlib-stage2: $(srcdir)/riscv-gcc stamps/build-newlib
 		--disable-shared \
 		--disable-threads \
 		--enable-languages=c,c++ \
-		--with-system-zlib \
+		@with_system_zlib@ \
 		--enable-tls \
 		--with-newlib \
 		--with-headers=$(INSTALL_DIR)/riscv$(XLEN)-unknown-elf/include \

configure

@@ -584,6 +584,7 @@ PACKAGE_URL=''
 
 ac_subst_vars='LTLIBOBJS
 LIBOBJS
+with_system_zlib
 configure_host
 cmodel
 gcc_checking
@@ -628,6 +629,7 @@ infodir
 docdir
 oldincludedir
 includedir
+runstatedir
 localstatedir
 sharedstatedir
 sysconfdir
@@ -658,6 +660,7 @@ enable_multilib
 enable_gcc_checking
 with_cmodel
 with_host
+with_system_zlib
 '
       ac_precious_vars='build_alias
 host_alias
@@ -705,6 +708,7 @@ datadir='${datarootdir}'
 sysconfdir='${prefix}/etc'
 sharedstatedir='${prefix}/com'
 localstatedir='${prefix}/var'
+runstatedir='${localstatedir}/run'
 includedir='${prefix}/include'
 oldincludedir='/usr/include'
 docdir='${datarootdir}/doc/${PACKAGE_TARNAME}'
@@ -957,6 +961,15 @@ do
   | -silent | --silent | --silen | --sile | --sil)
     silent=yes ;;
 
+  -runstatedir | --runstatedir | --runstatedi | --runstated \
+  | --runstate | --runstat | --runsta | --runst | --runs \
+  | --run | --ru | --r)
+    ac_prev=runstatedir ;;
+  -runstatedir=* | --runstatedir=* | --runstatedi=* | --runstated=* \
+  | --runstate=* | --runstat=* | --runsta=* | --runst=* | --runs=* \
+  | --run=* | --ru=* | --r=*)
+    runstatedir=$ac_optarg ;;
+
   -sbindir | --sbindir | --sbindi | --sbind | --sbin | --sbi | --sb)
     ac_prev=sbindir ;;
   -sbindir=* | --sbindir=* | --sbindi=* | --sbind=* | --sbin=* \
@@ -1094,7 +1107,7 @@ fi
 for ac_var in	exec_prefix prefix bindir sbindir libexecdir datarootdir \
 		datadir sysconfdir sharedstatedir localstatedir includedir \
 		oldincludedir docdir infodir htmldir dvidir pdfdir psdir \
-		libdir localedir mandir
+		libdir localedir mandir runstatedir
 do
   eval ac_val=\$$ac_var
   # Remove trailing slashes.
@@ -1247,6 +1260,7 @@ Fine tuning of the installation directories:
   --sysconfdir=DIR        read-only single-machine data [PREFIX/etc]
   --sharedstatedir=DIR    modifiable architecture-independent data [PREFIX/com]
   --localstatedir=DIR     modifiable single-machine data [PREFIX/var]
+  --runstatedir=DIR       modifiable per-process data [LOCALSTATEDIR/run]
   --libdir=DIR            object code libraries [EPREFIX/lib]
   --includedir=DIR        C header files [PREFIX/include]
   --oldincludedir=DIR     C header files for non-gcc [/usr/include]
@@ -1296,6 +1310,7 @@ Optional Packages:
   --with-host=x86_64-w64-mingw32
                           Sets the host for the tools, you probably want
                           nothing
+  --without-system-zlib   use the builtin copy of zlib from GCC
 
 Some influential environment variables:
   CC          C compiler command
@@ -3343,6 +3358,24 @@ else
 
 fi
 
+
+# Check whether --with-system-zlib was given.
+if test "${with_system_zlib+set}" = set; then :
+  withval=$with_system_zlib;
+else
+  with_system_zlib=yes
+
+fi
+
+
+if test "x$with_system_zlib" != xno; then :
+  with_system_zlib=--with-system-zlib
+
+else
+  with_system_zlib=--without-system-zlib
+
+fi
+
 cat >confcache <<\_ACEOF
 # This file is a shell script that caches the results of configure
 # tests run on this system so they can be shared between configure

configure.ac

@@ -135,4 +135,15 @@ AS_IF([test "x$with_host" != xdefault],
 	[AC_SUBST(configure_host,--host=$with_host)],
 	[AC_SUBST(configure_host,"")])
 
+AC_ARG_WITH(system-zlib,
+	[AS_HELP_STRING([--without-system-zlib],
+		[use the builtin copy of zlib from GCC])],
+	[],
+	[with_system_zlib=yes]
+	)
+
+AS_IF([test "x$with_system_zlib" != xno],
+	[AC_SUBST(with_system_zlib,--with-system-zlib)],
+	[AC_SUBST(with_system_zlib,--without-system-zlib)])
+
 AC_OUTPUT