allow CMAKE_BUILD_TYPE=PLD

--- llvm-3.8.0.src/CMakeLists.txt~	2016-01-13 21:03:44.000000000 +0200
+++ llvm-3.8.0.src/CMakeLists.txt	2016-10-01 15:54:42.749630541 +0300
@@ -174,11 +174,6 @@
 
 string(TOUPPER "${CMAKE_BUILD_TYPE}" uppercase_CMAKE_BUILD_TYPE)
 
-if (CMAKE_BUILD_TYPE AND
-    NOT uppercase_CMAKE_BUILD_TYPE MATCHES "^(DEBUG|RELEASE|RELWITHDEBINFO|MINSIZEREL)$")
-  message(FATAL_ERROR "Invalid value for CMAKE_BUILD_TYPE: ${CMAKE_BUILD_TYPE}")
-endif()
-
 set(LLVM_LIBDIR_SUFFIX "" CACHE STRING "Define suffix of library directory name (32/64)" )
 
 # They are used as destination of target generators.