Force Make into using a single thread

This also restricts fast-vapi's to Ninja. fast-vapi's improve build
performance when multi-threaded, but are bad when single-threaded.

Again emphasize that ninja-build should be used.

cmake/UseVala.cmake

@@ -118,7 +118,9 @@ function(vala_precompile output)
     cmake_parse_arguments(ARGS "FAST_VAPI" "DIRECTORY;GENERATE_HEADER;GENERATE_VAPI;EXPORTS_DIR"
         "SOURCES;PACKAGES;OPTIONS;DEFINITIONS;CUSTOM_VAPIS;GRESOURCES" ${ARGN})
 
-    set(ARGS_FAST_VAPI true)
+    if("Ninja" STREQUAL ${CMAKE_GENERATOR})
+        set(ARGS_FAST_VAPI true)
+    endif()
 
     if(ARGS_DIRECTORY)
         get_filename_component(DIRECTORY ${ARGS_DIRECTORY} ABSOLUTE)
@@ -274,7 +276,7 @@ function(vala_precompile output)
                 ${ARGS_CUSTOM_VAPIS}
                 ${ARGS_GRESOURCES}
             COMMENT
-                "Generating VAPI and headers for linking"
+                "Generating VAPI and headers for target ${output}"
             )
         endif()
     else(ARGS_FAST_VAPI)

configure

@@ -34,10 +34,9 @@ if ! [ -x "$exec_bin" ]; then
   make_bin="$(which make 2>/dev/null)"
   if [ -x "$make_bin" ]; then
     echo "-- Found Make: $make_bin"
-    echo "--   Using Ninja (ninja-build) might improve build experience."
     cmake_type="Unix Makefiles"
     exec_bin="$make_bin"
-    exec_command="$exec_bin -j4"
+    exec_command="$exec_bin"
   fi
 fi
 
@@ -95,3 +94,7 @@ default:
 %:
 	@sh -c "cd build; $exec_command \"\$@\""
 EOF
+
+if [[ "$exec_bin" == "$make_bin" ]]; then
+    echo "--   Running with make. Using Ninja (ninja-build) might improve build experience."
+fi