Give a test file a more sensible name so that it can hold more test cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126566 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/test/CodeGen/X86/phi-constants.ll b/test/CodeGen/X86/phi-bit-propagation.ll
similarity index 100%
rename from test/CodeGen/X86/phi-constants.ll
rename to test/CodeGen/X86/phi-bit-propagation.ll