fix build using cmake with generating version info from git

cmake/gitversion.cmake

@@ -0,0 +1,50 @@
+# Get commit hash
+execute_process(COMMAND git log --format='%H' -n 1
+	OUTPUT_VARIABLE GIT_COMMIT_HASH
+	ERROR_QUIET)
+# Check whether we got any revision (which isn't always the case, e.g. when
+# someone downloaded a zip file instead of a checkout)
+if ("${GIT_COMMIT_HASH}" STREQUAL "")
+	set(GIT_BRANCH "N/A")
+	set(GIT_COMMITS "")
+	set(GIT_COMMIT_HASH "N/A")
+	set(GIT_COMMIT_SHORT "N/A")
+	set(GIT_DIFF "")
+	set(GIT_TAG "N/A")
+else()
+	execute_process(COMMAND
+		bash -c "git diff --quiet --exit-code || echo +"
+		OUTPUT_VARIABLE GIT_DIFF)
+	execute_process(COMMAND
+		bash -c "git describe --always --tags |cut -f1 -d'-'"
+		OUTPUT_VARIABLE GIT_TAG ERROR_QUIET)
+	execute_process(COMMAND
+		bash -c "git describe --always --tags |cut -f2 -d'-'"
+		OUTPUT_VARIABLE GIT_COMMITS ERROR_QUIET)
+	execute_process(COMMAND
+		git rev-parse --abbrev-ref HEAD
+		OUTPUT_VARIABLE GIT_BRANCH)
+	string(STRIP "${GIT_COMMIT_HASH}" GIT_COMMIT_HASH)
+	string(SUBSTRING "${GIT_COMMIT_HASH}" 1 7 GIT_COMMIT_SHORT)
+	string(STRIP "${GIT_BRANCH}" GIT_BRANCH)
+	string(STRIP "${GIT_COMMITS}" GIT_COMMITS)
+	string(STRIP "${GIT_DIFF}" GIT_DIFF)
+	string(STRIP "${GIT_TAG}" GIT_TAG)
+endif()
+
+set(VERSION "const char* GIT_BRANCH=\"${GIT_BRANCH}\";
+const char* GIT_COMMIT=\"${GIT_COMMIT_SHORT}\";
+const char* GIT_COMMITS=\"${GIT_COMMITS}\";
+const char* GIT_TAG=\"${GIT_TAG}\";
+const char* VERSION=\"${GIT_TAG}-r${GIT_COMMITS}-g${GIT_COMMIT_SHORT}${GIT_DIFF}\";
+")
+
+message(DEBUG "Generated Version: \"${VERSION}\"")
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/version.h)
+	file(READ ${CMAKE_CURRENT_SOURCE_DIR}/version.h VERSION_)
+else()
+	set(VERSION_ "")
+endif()
+if (NOT "${VERSION}" STREQUAL "${VERSION_}")
+	file(WRITE "${CMAKE_CURRENT_SOURCE_DIR}/version.h" "${VERSION}")
+endif()