nightlies broken by implicit dependency on low-ptr-def.h

[Fred Emmott]

Fix (FB: D14243063):

diff --git a/hphp/ppc64-asm/CMakeLists.txt b/hphp/ppc64-asm/CMakeLists.txt
index 5d4c7c4539..013733becc 100644
--- a/hphp/ppc64-asm/CMakeLists.txt
+++ b/hphp/ppc64-asm/CMakeLists.txt
@@ -7,5 +7,6 @@ auto_sources(files "*.h" "${CMAKE_CURRENT_SOURCE_DIR}")
 list(APPEND HEADER_SOURCES ${files})
 
 add_library(ppc64-asm STATIC ${HEADERS_SOURCES} ${CXX_SOURCES})
+add_dependencies(ppc64-asm hphp_util)
 
 HHVM_PUBLIC_HEADERS(ppc64-asm ${HEADERS_SOURCES})