configure: support ZUO=<zuo>

Supplying `ZUO=<zuo>` skips the submodule check in `configure`
and configures the generated makefile not to build or remove Zuo.

BUILDING

@@ -149,7 +149,8 @@ information on the supported options.
 The generated makefile mostly just ensures that a `zuo` executable is
 built in a `bin` directory, and then it defers the actual build work
 to `zuo`, which uses the "main.zuo" file. If you have `zuo` installed,
-you can use `zuo` directly instead of `make`. In general, instead of
+you can use `zuo` directly instead of `make`: in that case, you may
+wish to use `./configure ZUO=<zuo>`. In general, instead of
 the command `make X` to build target `X` as described below, you can
 use `zuo . X` (or `bin/zuo . X` after `bin/zuo` is built).
 
@@ -333,7 +334,7 @@ The makefile supports several targets:
  * `make clean`
 
    Removes all built elements from the workarea, and then removes
-   `bin/zuo`.
+   `bin/zuo` (unless configured with `ZUO=<zuo>`).
 
 
 WINDOWS VIA COMMAND PROMPT

configure

@@ -103,6 +103,7 @@ moreBootFiles=
 preloadBootFiles=
 alwaysUseBootFile=
 skipSubmoduleUpdate=
+zuoExternal=
 
 CONFIG_UNAME=`uname`
 
@@ -446,6 +447,9 @@ while [ $# != 0 ] ; do
     LZ4=*)
       LZ4Lib=`echo $1 | sed -e 's/^LZ4=//'`
       ;;
+    ZUO=*)
+      zuoExternal=`echo $1 | sed -e 's/^ZUO=//'`
+      ;;
     *)
       echo "option '$1' unrecognized or missing an argument; try $0 --help"
       exit 1
@@ -672,6 +676,7 @@ if [ "$help" = "yes" ]; then
   echo "  STRIP=<strip>                     executable stripper"
   echo "  ZLIB=<lib>                        link to <lib> instead of own zlib"
   echo "  LZ4=<lib>                         link to <lib> instead of own LZ4"
+  echo "  ZUO=<zuo>                         build with <zuo> instead of own Zuo"
   echo ""
   echo "Available machine types: $machs"
   echo ""
@@ -889,8 +894,17 @@ submod_instructions () {
     exit 1
 }
 
-if [ ! -f "$srcdir"/zuo/configure ] ; then
-    submod_instructions 'Source in "zuo" is missing'
+if [ "${zuoExternal}" = "" ] ; then
+    if [ ! -f "$srcdir"/zuo/configure ] ; then
+        submod_instructions 'Source in "zuo" is missing'
+    fi
+    ZUO="bin/zuo"
+    RM_ZUO="rm -f bin/zuo"
+    ZUO_TARGET="bin/zuo"
+else
+    ZUO="${zuoExternal}"
+    RM_ZUO="@echo 'Not cleaning external ${zuoExternal}'"
+    ZUO_TARGET="DoNotBuildZuo"
 fi
 
 if [ ! -f "$srcdir"/nanopass/nanopass.ss ] ; then
@@ -1130,6 +1144,10 @@ preloadBootFiles=$preloadBootFiles
 alwaysUseBootFile=$alwaysUseBootFile
 relativeBootFiles=$relativeBootFiles
 
+ZUO=$ZUO
+RM_ZUO=$RM_ZUO
+ZUO_TARGET=$ZUO_TARGET
+
 InstallBin=$installbin
 InstallLib=$installlib
 InstallMan=$installman/man1

makefiles/Makefile.in

@@ -3,8 +3,6 @@ workarea=$(w)
 
 include $(workarea)/Mf-config
 
-ZUO=bin/zuo
-
 .PHONY: build
 build: $(ZUO)
 	+ $(ZUO) $(workarea) MAKE="$(MAKE)"
@@ -144,9 +142,9 @@ pkg: $(ZUO)
 .PHONY: clean
 clean: $(ZUO)
 	+ $(ZUO) $(workarea) clean MAKE="$(MAKE)"
-	rm -f bin/zuo
+	$(RM_ZUO)
 
 # Using `+` here means that $(ZUO) gets built even if `-n`/`--dry-run` is provided to `make`
-$(ZUO): $(srcdir)/zuo/zuo.c
+$(ZUO_TARGET): $(srcdir)/zuo/zuo.c
 	+ mkdir -p bin
 	+ $(CC_FOR_BUILD) -DZUO_LIB_PATH='"'"../zuo/lib"'"' -o $(ZUO) $(srcdir)/zuo/zuo.c