Don't default the *cached* list of targets to build to an explicit list

of the targets we know about. Because this is cached, rebuilds won't
detect when new targets show up. It's also a bit simpler to just say
"all". If users want to restrict the target set, they can still do so,
and then the cache will preserve what they have explicitly set this
field to.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@146467 91177308-0d34-0410-b5e6-96231b3b80d8

CMakeLists.txt

@@ -90,7 +90,7 @@ if( MSVC )
   set(LLVM_TARGETS_TO_BUILD X86
     CACHE STRING "Semicolon-separated list of targets to build, or \"all\".")
 else( MSVC )
-  set(LLVM_TARGETS_TO_BUILD ${LLVM_ALL_TARGETS}
+  set(LLVM_TARGETS_TO_BUILD "all"
     CACHE STRING "Semicolon-separated list of targets to build, or \"all\".")
 endif( MSVC )