Add build flag for disable http transport

cmake/SelectHTTP.cmake

@@ -0,0 +1,32 @@
+include(SanitizeInput)
+
+if(USE_HTTP STREQUAL "")
+	set(USE_HTTP ON)
+endif()
+
+sanitizeinput(USE_HTTP)
+
+if(USE_HTTP STREQUAL ON)
+	set(GIT_HTTP 1)
+	add_feature_info(HTTP ON "HTTP transport support")
+elseif(USE_HTTP STREQUAL OFF)
+	# Several features only have meaning over HTTP: HTTPS, NTLM and
+	# Negotiate auth. If the user did not request them explicitly, silently
+	# disable them to keep configurations consistent. If they were requested
+	# explicitly, error out: they cannot be built without the HTTP transport.
+	foreach(_dep USE_HTTPS USE_AUTH_NTLM USE_AUTH_NEGOTIATE)
+		if(${_dep} STREQUAL "")
+			set(${_dep} OFF)
+		else()
+			set(_dep_check "${${_dep}}")
+			sanitizeinput(_dep_check)
+			if(_dep_check)
+				message(FATAL_ERROR "${_dep}=${${_dep}} requires USE_HTTP=ON; this feature depends on the HTTP transport")
+			endif()
+		endif()
+	endforeach()
+
+	add_feature_info(HTTP OFF "HTTP transport support is disabled")
+else()
+	message(FATAL_ERROR "unknown HTTP option: ${USE_HTTP}")
+endif()