clar: introduce CLAR_XML option

Introduce a CLAR_XML option, to run the `ctest` commands with the new
`-r` flag to clar.  Permitted values are `OFF`, `ON` and a directory to
write the XML test results to.

(cherry picked from commit a2d73f56)

CMakeLists.txt

@@ -44,6 +44,8 @@ OPTION( USE_GSSAPI			"Link with libgssapi for SPNEGO auth"   OFF )
 OPTION( VALGRIND			"Configure build for valgrind"			OFF )
 OPTION( CURL			"Use curl for HTTP if available" ON)
 OPTION( DEBUG_POOL			"Enable debug pool allocator"			OFF )
+   SET( CLAR_XML 			"OFF"					       CACHE STRING
+       "Writes test results in XML format.  One of ON, OFF or the directory to write to; this does not affect the output executables, this only affects the behavior of the ctest command.")
 
 IF(DEBUG_POOL)
 	ADD_DEFINITIONS(-DGIT_DEBUG_POOL)
@@ -704,11 +706,25 @@ IF (BUILD_CLAR)
 
 	ENABLE_TESTING()
 
-	ADD_TEST(offline   libgit2_clar -v -xonline)
-	ADD_TEST(online    libgit2_clar -v -sonline)
-	ADD_TEST(gitdaemon libgit2_clar -v -sonline::push)
-	ADD_TEST(ssh       libgit2_clar -v -sonline::push -sonline::clone::ssh_cert -sonline::clone::ssh_with_paths)
-	ADD_TEST(proxy     libgit2_clar -v -sonline::clone::proxy_credentials_in_url -sonline::clone::proxy_credentials_request)
+	IF (CLAR_XML)
+		IF (CLAR_XML STREQUAL "ON")
+			SET(XML_PATH "")
+		ELSE ()
+			SET(XML_PATH "${CLAR_XML}/")
+		ENDIF ()
+
+		SET(TESTS_OFFLINE_XML   "-r${XML_PATH}results_offline.xml")
+		SET(TESTS_ONLINE_XML    "-r${XML_PATH}results_online.xml")
+		SET(TESTS_GITDAEMON_XML "-r${XML_PATH}results_gitdaemon.xml")
+		SET(TESTS_SSH_XML       "-r${XML_PATH}results_ssh.xml")
+		SET(TESTS_PROXY_XML     "-r${XML_PATH}results_proxy.xml")
+	ENDIF ()
+
+	ADD_TEST(offline   libgit2_clar -v ${TESTS_OFFLINE_XML} -xonline)
+	ADD_TEST(online    libgit2_clar -v ${TESTS_ONLINE_XML} -sonline)
+	ADD_TEST(gitdaemon libgit2_clar -v ${TESTS_GITDAEMON_XML} -sonline::push)
+	ADD_TEST(ssh       libgit2_clar -v ${TESTS_SSH_XML} -sonline::push -sonline::clone::ssh_cert -sonline::clone::ssh_with_paths)
+	ADD_TEST(proxy     libgit2_clar -v ${TESTS_PROXY_XML} -sonline::clone::proxy_credentials_in_url -sonline::clone::proxy_credentials_request)
 ENDIF ()
 
 IF (TAGS)