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()
-
 # LLVM_INSTALL_PACKAGE_DIR needs to be declared prior to adding the tools
 # subdirectory in order to have the value available for llvm-config.
 include(GNUInstallPackageDir)