cmake: document CMakeLists.txt hierarchy

CMakeLists.txt

-# CMake build script for the libgit2 project
+# libgit2: the cross-platform, linkable library implementation of git.
 # See `README.md` for build instructions.
+#
+# This top-level CMakeLists.txt sets up configuration options and
+# determines which subprojects to build.
 
 cmake_minimum_required(VERSION 3.5.1)
 

examples/CMakeLists.txt

+# examples: code usage examples of libgit2
+
 file(GLOB SRC_EXAMPLES *.c *.h)
 
 add_executable(lg2 ${SRC_EXAMPLES})

fuzzers/CMakeLists.txt

+# fuzzers: libFuzzer and standalone fuzzing utilities
+
 if(BUILD_FUZZERS AND NOT USE_STANDALONE_FUZZERS)
 	set(CMAKE_REQUIRED_FLAGS "-fsanitize=fuzzer-no-link")
 	add_c_flag(-fsanitize=fuzzer)

src/libgit2/CMakeLists.txt

+# libgit2: the shared library: this CMakeLists.txt compiles the core
+# git library functionality.
+
 add_library(git2internal OBJECT)
 set_target_properties(git2internal PROPERTIES C_STANDARD 90)
 set_target_properties(git2internal PROPERTIES C_EXTENSIONS OFF)

src/util/CMakeLists.txt

@@ -54,6 +54,7 @@ list(SORT UTIL_SRC_HASH)
 #
 
 target_sources(util PRIVATE ${UTIL_SRC} ${UTIL_SRC_OS} ${UTIL_SRC_HASH})
+ide_split_sources(util)
 
 target_include_directories(util PRIVATE ${UTIL_INCLUDES} ${LIBGIT2_DEPENDENCY_INCLUDES} PUBLIC ${libgit2_SOURCE_DIR}/include)
 target_include_directories(util SYSTEM PRIVATE ${LIBGIT2_SYSTEM_INCLUDES})

tests/CMakeLists.txt

+# tests: the unit and integration tests for libgit2
+
 set(Python_ADDITIONAL_VERSIONS 3 2.7)
 find_package(PythonInterp)