CMake: allow appending a string to the library filename

This helps us install multiple versions of the library side-by-side.

CMakeLists.txt

@@ -24,6 +24,7 @@ OPTION( BUILD_EXAMPLES		"Build library usage example apps"		OFF )
 OPTION( TAGS				"Generate tags"							OFF )
 OPTION( PROFILE				"Generate profiling information"		OFF )
 OPTION( ENABLE_TRACE		"Enables tracing support"				OFF )
+OPTION( SONAME_APPEND "Append the given string to the library's filename" OFF )
 IF(MSVC)
 	# This option is only availalbe when building with MSVC. By default,
 	# libgit2 is build using the stdcall calling convention, as that's what
@@ -304,6 +305,9 @@ MSVC_SPLIT_SOURCES(git2)
 IF (SONAME)
 	SET_TARGET_PROPERTIES(git2 PROPERTIES VERSION ${LIBGIT2_VERSION_STRING})
 	SET_TARGET_PROPERTIES(git2 PROPERTIES SOVERSION ${LIBGIT2_VERSION_MAJOR})
+	IF (SONAME_APPEND)
+		SET_TARGET_PROPERTIES(git2 PROPERTIES OUTPUT_NAME "git2-${SONAME_APPEND}")
+	ENDIF()
 ENDIF()
 CONFIGURE_FILE(${CMAKE_CURRENT_SOURCE_DIR}/libgit2.pc.in ${CMAKE_CURRENT_BINARY_DIR}/libgit2.pc @ONLY)