Harmonise passing build version

Avoid running some configure step, instead pass it as a define like the Makefile

src/.gitignore

@@ -1,2 +0,0 @@
-# Generated by CMake
-/.version.cpp

src/CMakeLists.txt

@@ -9,8 +9,9 @@ add_library(common OBJECT
     "style.cpp"
     "usage.cpp"
     "util.cpp"
-    "_version.cpp"
+    "version.cpp"
 )
+target_compile_definitions(common PRIVATE "BUILD_VERSION_STRING=\"${GIT_REV}\"")
 
 find_package(BISON 3.0.0 REQUIRED)
 set(BISON_FLAGS "-Wall -Dlr.type=ielr")

src/version.cpp

@@ -25,13 +25,6 @@ extern "C" {
 }
 #endif
 
-// This variable is passed via `-D` from the Makefile, but not from CMake
-// (in which `configure_file()` is used on this file to replace some syntax)
-#ifndef BUILD_VERSION_STRING
-    // CMake-specific syntax here
-	#define BUILD_VERSION_STRING "@GIT_REV@"
-#endif
-
 char const *get_package_version_string() {
 	if constexpr (literal_strlen(BUILD_VERSION_STRING) > 0) {
 		return BUILD_VERSION_STRING;