diff -urNp -x '*.orig' llvm-11.0.1.src.org/CMakeLists.txt llvm-11.0.1.src/CMakeLists.txt
--- llvm-11.0.1.src.org/CMakeLists.txt	2021-03-25 22:28:14.616795886 +0100
+++ llvm-11.0.1.src/CMakeLists.txt	2021-03-25 22:28:19.786759915 +0100
@@ -264,11 +264,6 @@ endif()
 
 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)" )
 
 set(LLVM_TOOLS_INSTALL_DIR "bin" CACHE STRING "Path for binary subdirectory (defaults to 'bin')")