Merge remote-tracking branch 'remotes/bonzini/configure' into staging

Merge remote-tracking branch 'remotes/bonzini/configure' into staging

* remotes/bonzini/configure:
  build: softmmu targets do not have a "main.o" file
  configure: Disable libtool if -fPIE does not work with it (bug #1257099)
  block: convert block drivers linked with libs to modules
  Makefile: introduce common-obj-m and block-obj-m for DSO
  Makefile: install modules with "make install"
  module: implement module loading
  rules.mak: introduce DSO rules
  darwin: do not use -mdynamic-no-pic
  block: use per-object cflags and libs
  rules.mak: allow per object cflags and libs
  rules.mak: fix $(obj) to a real relative path
  util: Split out exec_dir from os_find_datadir

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>