VWR-20911 FIXED CMake build arch detection is inaccurate and incomplete

Robin Cornelius' patch from
http://jira.secondlife.com/secure/attachment/42801/SNOW-776+Don%27t+use+uname+for+build+arch+detection%2C+use+compiler.patch
applied without fuzz:

	patching file indra/cmake/Variables.cmake
	Hunk #1 succeeded at 52 (offset -2 lines).

Added entry in doc/contributions.txt.
No further changes other than that.
(transplanted from a9132a63e4739965d65ddd58a7be9eabe4321c2a)

doc/contributions.txt

@@ -563,6 +563,7 @@ Robin Cornelius
 	VWR-12758
 	VWR-12763
 	VWR-12995
+	VWR-20911
 Ryozu Kojima
 	VWR-53
 	VWR-287

indra/cmake/Variables.cmake

@@ -54,19 +54,20 @@ if (${CMAKE_SYSTEM_NAME} MATCHES "Linux")
   set(LINUX ON BOOl FORCE)
 
   # If someone has specified a word size, use that to determine the
-  # architecture.  Otherwise, let the architecture specify the word size.
+  # architecture.  Otherwise, let the compiler specify the word size.
+  # Using uname will break under chroots and other cross arch compiles. RC
   if (WORD_SIZE EQUAL 32)
     set(ARCH i686)
   elseif (WORD_SIZE EQUAL 64)
     set(ARCH x86_64)
   else (WORD_SIZE EQUAL 32)
-    execute_process(COMMAND uname -m COMMAND sed s/i.86/i686/
-                    OUTPUT_VARIABLE ARCH OUTPUT_STRIP_TRAILING_WHITESPACE)
-    if (ARCH STREQUAL x86_64)
-      set(WORD_SIZE 64)
-    else (ARCH STREQUAL x86_64)
-      set(WORD_SIZE 32)
-    endif (ARCH STREQUAL x86_64)
+    if(CMAKE_SIZEOF_VOID_P MATCHES 4)
+ 		set(ARCH i686)
+		set(WORD_SIZE 32)
+	else(CMAKE_SIZEOF_VOID_P MATCHES 4)
+		set(ARCH x86_64)
+		set(WORD_SIZE 64)
+	endif(CMAKE_SIZEOF_VOID_P MATCHES 4)
   endif (WORD_SIZE EQUAL 32)
 
   set(LL_ARCH ${ARCH}_linux)