always disable imap gss
see: https://github.com/facebook/hhvm/pull/1181#issuecomment-27153815
--- hhvm-HHVM-2.3.2/CMake/HPHPFindLibs.cmake~	2013-12-23 22:51:42.000000000 +0200
+++ hhvm-HHVM-2.3.2/CMake/HPHPFindLibs.cmake	2014-01-02 00:52:37.828252903 +0200
@@ -308,10 +308,10 @@
 find_package(Libpam)
 if (PAM_INCLUDE_PATH)
 	include_directories(${PAM_INCLUDE_PATH})
-else()
-	add_definitions(-DSKIP_IMAP_GSS=1)
 endif()
 
+add_definitions(-DSKIP_IMAP_GSS=1)
+
 if (EXISTS "${CCLIENT_INCLUDE_PATH}/linkage.c")
 	CONTAINS_STRING("${CCLIENT_INCLUDE_PATH}/linkage.c" ssl_onceonlyinit CCLIENT_HAS_SSL)
 endif()