Add required scaffolding for libbpf

Add a find module for libbpf and link libbpf to HHVM artifacts.

Author: mszabo-wikia

CMake/FindBpf.cmake

@@ -0,0 +1,15 @@
+find_path(BPF_INCLUDE_DIR bpf/bpf.h)
+find_library(BPF_LIBRARY NAMES bpf)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(BPF DEFAULT_MSG BPF_LIBRARY BPF_INCLUDE_DIR)
+
+if(BPF_FOUND)
+  set(BPF_LIBRARIES ${BPF_LIBRARY})
+  set(BPF_INCLUDE_DIRS ${BPF_INCLUDE_DIR})
+else()
+  set(BPF_LIBRARIES)
+  set(BPF_INCLUDE_DIRS)
+endif()
+
+mark_as_advanced(BPF_LIBRARIES BPF_INCLUDE_DIRS)

CMake/HPHPFindLibs.cmake

@@ -271,6 +271,10 @@ if (APPLE)
   find_library(KERBEROS_LIB NAMES gssapi_krb5)
 endif()
 
+if (LINUX)
+  find_package(Bpf REQUIRED)
+endif()
+
 # This is required by Homebrew's libc. See
 # https://github.com/facebook/hhvm/pull/5728#issuecomment-124290712
 # for more info.
@@ -332,6 +336,10 @@ macro(hphp_link target)
   target_link_libraries(${target} ${VISIBILITY} ${CURL_LIBRARIES})
   target_link_libraries(${target} ${VISIBILITY} glog)
 
+  if (LINUX)
+    target_link_libraries(${target} ${VISIBILITY} ${BPF_LIBRARIES})
+  endif()
+
   if (LIBINOTIFY_LIBRARY)
     target_link_libraries(${target} ${VISIBILITY} ${LIBINOTIFY_LIBRARY})
   endif()