cmake: Allow to configure GGML_BUILD_NUMBER with file

This will enable llama-cpp-python to generate the file during sdist
build and include it into the final tarball. The file then will be
picked up by the package build to include the correct version, even
without full git checkout included.

Related: abetlen/llama-cpp-python#1979

Signed-off-by: Ihar Hrachyshka <[email protected]>

Author: booxter

Diff for: ggml/CMakeLists.txt

@@ -287,6 +287,15 @@ endif()
 
 # Generate version info based on git commit.
 
+# First try to get the build number from the file.
+if(NOT DEFINED GGML_BUILD_NUMBER)
+    if(EXISTS ${CMAKE_SOURCE_DIR}/.ggml_build_number)
+        file(STRINGS ${CMAKE_SOURCE_DIR}/.ggml_build_number GGML_BUILD_NUMBER)
+        # Assume the first line contains the desired version.
+        list(GET GGML_BUILD_NUMBER 0 GGML_BUILD_NUMBER)
+    endif()
+endif()
+
 if(NOT DEFINED GGML_BUILD_NUMBER)
     find_program(GIT_EXE NAMES git git.exe REQUIRED NO_CMAKE_FIND_ROOT_PATH)
     execute_process(COMMAND ${GIT_EXE} rev-list --count HEAD