workaround old version of /bin/date in msysgit

fails with "invalid date `@1406586781'"
Fix build on LLVM 3.5

Patch by @crayxt
do not call __init__ for code loaded during system image build
fixes #7723

part of this refactors jl_module_run_initializer to only run the
initializer and not do anything else, which seems like a good idea.
Add overlooked LLVM_MFLAGS to (re)install-llvm
update NEWS and help
By popular demand, GCC has been snatched from the jaws of oblivion