[compiler-rt] list_union() is actually an intersect operation. Rename it.

Summary:
Given:
  set(T1 a b c)
  set(T2 b c d)
  message("T1=${T1}")
  message("T2=${T2}")
  list_union(T3 T1 T2)
  message("T3=${T3}")
cmake emitted:
  T1=a;b;c
  T2=b;c;d
  T3=b;c

Reviewers: beanz

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D16580

llvm-svn: 258916
diff --git a/compiler-rt/cmake/Modules/AddCompilerRT.cmake b/compiler-rt/cmake/Modules/AddCompilerRT.cmake
index 4c2d330..660488d 100644
--- a/compiler-rt/cmake/Modules/AddCompilerRT.cmake
+++ b/compiler-rt/cmake/Modules/AddCompilerRT.cmake
@@ -19,7 +19,7 @@
       set(libname "${name}.${os}")
       set(libnames ${libnames} ${libname})
       set(extra_cflags_${libname} ${DARWIN_${os}_CFLAGS})
-      list_union(LIB_ARCHS_${libname} DARWIN_${os}_ARCHS LIB_ARCHS)
+      list_intersect(LIB_ARCHS_${libname} DARWIN_${os}_ARCHS LIB_ARCHS)
     endforeach()
   else()
     foreach(arch ${LIB_ARCHS})
@@ -87,7 +87,7 @@
         set(libname "${name}_${os}_dynamic")
         set(extra_linkflags_${libname} ${DARWIN_${os}_LINKFLAGS} ${LIB_LINKFLAGS})
       endif()
-      list_union(LIB_ARCHS_${libname} DARWIN_${os}_ARCHS LIB_ARCHS)
+      list_intersect(LIB_ARCHS_${libname} DARWIN_${os}_ARCHS LIB_ARCHS)
       if(LIB_ARCHS_${libname})
         list(APPEND libnames ${libname})
         set(extra_cflags_${libname} ${DARWIN_${os}_CFLAGS} ${LIB_CFLAGS})