Introduce parallelism

By using --cores argument to rootfs.py, JOBS= is set in the
live-bootstrap environment, and -j${JOBS} is used on builds. This speeds
larger packages up significantly.

A fair number of packages do not build properly with parallelism. Most
of these, at least for now, are disabled with -j1.

sysc/python-3.4.10/python-3.4.10.sh

@@ -58,9 +58,9 @@ src_configure() {
 
 src_compile() {
     # Build pgen
-    make Parser/pgen
+    make -j1 Parser/pgen
     # Regen graminit.c and graminit.h
-    make Include/graminit.h
+    make "${MAKEJOBS}" Include/graminit.h
 
     # Regenerate some Python scripts using the other regenerated files
     # Must move them out to avoid using Lib/ module files which are
@@ -72,7 +72,7 @@ src_compile() {
     python token.py
 
     # Now build the main program
-    make CFLAGS="-U__DATE__ -U__TIME__"
+    make "${MAKEJOBS}" CFLAGS="-U__DATE__ -U__TIME__"
 }
 
 src_install() {