Commit Briefs
all: remove $OBJTYPE from build
Now that we assume pthreads, the only assembly left is in libmp and libsec. We only ever added assembly for 386. The portable C code is fine for plan9port.
9c, 9l: accept CC9FLAGS from config
Also, if CC9FLAGS includes -fsanitize=address (ASAN), predefine PLAN9PORT_ASAN for use by programs that need to know (mainly libthread). The 9c script used to have a variable called ngflags, which was ccflags except -g (ng stood for "no g"), but nothing needs it split out anymore, so simplify to just ccflags.
all: remove Linux 2.4 vs 2.6 detection
Linux 2.4 is dead. (The libthread code hasn't worked for Linux 2.4 for a long time.)
9c, 9l: use $TMPDIR if available (#272)
NixOS sandboxed builds (at least on Mac) don't have access to /tmp, and this should be better POSIX.
9l: support Linux version 5.0+ (#274)
Update 9l to support Linux 5.x.
9l: accept Linux kernel version 4.x
Fixes #114.
9l: link with -lresolv on Linux
LGTM=rsc R=rsc https://codereview.appspot.com/136520044