Parallelize randomx compile and print some timings

When using "./build.sh -jX" we now pass the number of jobs to use
to the RandomX compilation which greatly speeds it up.

util/build.sh

@@ -128,7 +128,7 @@ ld -v
 
 HOST="$HOST" BUILD="$BUILD" "$MAKE" "$@" -C ./depends/ V=1
 
-./autogen.sh
+time ./autogen.sh
 
 CONFIG_SITE="$PWD/depends/$HOST/share/config.site" ./configure "$HARDENING_ARG" "$LCOV_ARG" "$TEST_ARG" "$MINING_ARG" $CONFIGURE_FLAGS CXXFLAGS='-g'
 
@@ -147,9 +147,10 @@ then
 else
     mkdir build && cd build
     cmake -DARCH=native ..
-    make
+    # pass along potential -jX and other args
+    time make "$@"
 fi
 
 cd $WD
 
-"$MAKE" "$@" V=1
+time "$MAKE" "$@" V=1