check for existence before cloning

Author: tkelman

support/cygwin_juliadev.ps1

@@ -1,14 +1,17 @@
-(new-object net.webclient).DownloadFile("http://cygwin.com/setup-x86_64.exe", "C:\cygwin\setup-x86_64.exe")
+(new-object net.webclient).DownloadFile(
+  "http://cygwin.com/setup-x86_64.exe", "C:\cygwin\setup-x86_64.exe")
 foreach ($pkg in @("make","curl","patch","python","gcc-g++","m4","p7zip",
     "mingw64-i686-gcc-g++","mingw64-i686-gcc-fortran",
     "mingw64-x86_64-gcc-g++","mingw64-x86_64-gcc-fortran")) {
   Write-Host $("Installing "+$pkg)
   & C:\cygwin\setup-x86_64.exe -q -n -g -P $pkg >$null 2>&1
 }
-& git config --global core.autocrlf input
-C:\cygwin\bin\sh -lc "git clone git://github.com/JuliaLang/julia.git julia32 && \
-  cd julia32 && git submodule init && git submodule update && \
-  XC_HOST=i686-w64-mingw32 make -j2 -C deps"
-C:\cygwin\bin\sh -lc "git clone git://github.com/JuliaLang/julia.git julia64 && \
-  cd julia64 && git submodule init && git submodule update && \
-  XC_HOST=x86_64-w64-mingw32 make -j2 -C deps"
+C:\cygwin\bin\sh -lc "git config --global core.autocrlf input"
+C:\cygwin\bin\sh -lc "if ! [ -e julia32 ]; then git clone \
+  git://github.com/JuliaLang/julia.git julia32; fi && \
+  cd julia32 && git submodule init && git pull && \
+  git submodule update && XC_HOST=i686-w64-mingw32 make -C deps"
+C:\cygwin\bin\sh -lc "if ! [ -e julia64 ]; then git clone \
+  git://github.com/JuliaLang/julia.git julia64; fi && \
+  cd julia64 && git submodule init && git pull && \
+  git submodule update && XC_HOST=x86_64-w64-mingw32 make -C deps"