Fix CMake rules when nesting CMake projects
`${CMAKE_SOURCE_DIR}` points to the outer project root, not the current directory.
Fixes building of `glslang` when included into another CMake project.
diff --git a/CMakeLists.txt b/CMakeLists.txt
index daf8739..29b39fb 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -237,9 +237,9 @@
################################################################################
# Build version information generation
################################################################################
-set(GLSLANG_CHANGES_FILE "${CMAKE_SOURCE_DIR}/CHANGES.md")
-set(GLSLANG_BUILD_INFO_PY "${CMAKE_SOURCE_DIR}/build_info.py")
-set(GLSLANG_BUILD_INFO_H_TMPL "${CMAKE_SOURCE_DIR}/build_info.h.tmpl")
+set(GLSLANG_CHANGES_FILE "${CMAKE_CURRENT_SOURCE_DIR}/CHANGES.md")
+set(GLSLANG_BUILD_INFO_PY "${CMAKE_CURRENT_SOURCE_DIR}/build_info.py")
+set(GLSLANG_BUILD_INFO_H_TMPL "${CMAKE_CURRENT_SOURCE_DIR}/build_info.h.tmpl")
set(GLSLANG_BUILD_INFO_H "${GLSLANG_GENERATED_INCLUDEDIR}/glslang/build_info.h")
# Command to build the build_info.h file
