[cmake] Add LLVM_BUILD_DEBUG to llvm-config.h

Some LLVM libraries may conditionally define some class members
depending on whether LLVM build type == Debug.
However, relying on `NDEBUG` for this may create situations in
which the consumer of a header in a downstream project has a
different definition for `NDEBUG`, resulting in an ODR violation.

The use of `LLVM_BUILD_DEBUG` should be preferred in these cases.

Author: jalopezg-git

llvm/CMakeLists.txt

@@ -492,6 +492,11 @@ set(LLVM_LIBRARY_DIR      ${LLVM_LIBRARY_OUTPUT_INTDIR}) # --libdir
 set(LLVM_MAIN_SRC_DIR     ${CMAKE_CURRENT_SOURCE_DIR}  ) # --src-root
 set(LLVM_MAIN_INCLUDE_DIR ${LLVM_MAIN_SRC_DIR}/include ) # --includedir
 set(LLVM_BINARY_DIR       ${CMAKE_CURRENT_BINARY_DIR}  ) # --prefix
+if( uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG" )
+  set(LLVM_BUILD_DEBUG ON)
+else()
+  set(LLVM_BUILD_DEBUG OFF)
+endif()
 
 
 # Note: LLVM_CMAKE_DIR does not include generated files

llvm/include/llvm/Config/llvm-config.h.cmake

@@ -104,6 +104,9 @@
 /* Define to 1 if you have the <sysexits.h> header file. */
 #cmakedefine HAVE_SYSEXITS_H ${HAVE_SYSEXITS_H}
 
+/* Define if this LLVM build is a Debug build */
+#cmakedefine LLVM_BUILD_DEBUG
+
 /* Define if building libLLVM shared library */
 #cmakedefine LLVM_BUILD_LLVM_DYLIB