Allow user to specify arch for fetch_Third_Party.bat. Refs #6527

Code/fetch_Third_Party.bat

 :: This script deals with getting hold of the required third party includes and libraries
 :: It will either clone or pull 3rdpartyincludes & 3rdpartylibs-win32/64 and put them in the right place for CMake
-:: Your architecture is auto-determined
-
+::
+:: Usage: fetch_Third_Party [win32|win64]
+::
+::    - [x86|x64] If provided this indicates the required architecture. If left bank your architecture is auto-determined
 @echo off
 
-:: Check for git. Older versions used %GitCmd%, newer just git
+:: Check for git. Older versions used %GitCmd%, newer just git. The older versions still 
+:: have git.exe but it should be called through git.cmd so git.cmd check is first
 echo Checking for git.cmd
 for %%X in (git.cmd) do (set FOUND=%%~$PATH:X)
 if defined FOUND (
@@ -16,16 +19,19 @@ if defined FOUND (
         set GitCmd=git.exe
     ) else (
         echo Cannot find git. Make sure the cmd folder is in your path.
-        exit /b 1
+        exit 1
     )
 )
 echo Using %GitCmd%
 
+:: It would seem that the %ERRORLEVEL% is not set correctly when inside an if statement
+:: so we have to do the check for the OS arch and then override it with the user provided value if necessary
+
 :: Check whether we're 64 or 32 bit. Store it in the 'arch' variable
-Set RegQry=HKLM\Hardware\Description\System\CentralProcessor\0
+set RegQry=HKLM\Hardware\Description\System\CentralProcessor\0
  
 REG.exe Query %RegQry% > checkOS.txt
- 
+
 Find /i "x86" < CheckOS.txt > StringCheck.txt
  
 If %ERRORLEVEL% == 0 (
@@ -33,11 +39,26 @@ If %ERRORLEVEL% == 0 (
 ) ELSE (
     set arch=win64
 )
-
 :: Remove temporary files created above
 del CheckOS.txt
 del StringCheck.txt
 
+:: Check if user has overridden the value
+if NOT "%1"=="" (
+  if "%1"=="win64" (
+    set arch=win64
+  ) else (
+    if "%1"=="win32" (
+      set arch=win32
+    ) else (
+     echo "Unknown architecture. Valid options are:win32,win64."
+      exit 1
+    )
+  )
+)
+echo Using architecture=%arch%
+
+
 :: Find out the url where mantid came from so we use the same location & protocol
 FOR /F %%I IN ('%GitCmd% config --get remote.origin.url') DO SET url=%%I
 echo Mantid repository URL: %url%