Bug 1259382 - Get a full path to the compiler wrapper. r=ted

In the near future, we are going to try running the compiler wrapper
from python code, and that will work better if we have the full path
to it.

build/moz.configure/toolchain.configure

@@ -97,13 +97,22 @@ set_config('MOZ_USING_CCACHE', using_ccache)
 @depends('--with-compiler-wrapper', ccache)
 @imports(_from='mozbuild.shellutil', _import='split', _as='shell_split')
 def compiler_wrapper(wrapper, ccache):
+    if wrapper:
+        raw_wrapper = wrapper[0]
+        wrapper = shell_split(raw_wrapper)
+        wrapper_program = find_program(wrapper[0])
+        if not wrapper_program:
+            die('Cannot find `%s` from the given compiler wrapper `%s`',
+                wrapper[0], raw_wrapper)
+        wrapper[0] = wrapper_program
+
     if ccache:
         if wrapper:
-            return tuple([ccache] + shell_split(wrapper[0]))
+            return tuple([ccache] + wrapper)
         else:
             return (ccache,)
     elif wrapper:
-        return tuple(shell_split(wrapper[0]))
+        return tuple(wrapper)
 
 add_old_configure_assignment('COMPILER_WRAPPER', compiler_wrapper)