[R-SIG-Win] An update on the windows toolchain developments

[Jeroen Ooms]

A new version of the toolchain based on gcc 4.9.3 and corresponding
build of R-devel are available from [1]. See the readme.txt [2] for
details. The installer should work out of the box and make it easy for
Windows users to compile and test R packages with the new toolchain.

The bad news: unfortunately it appears that the sjlj problem on win64
(triggered by Rf_error) is still not completely solved in the latest
mingw-w64. Therefore I restored -fno-asynchronous-unwind-tables in
CXXFLAGS in the latest build of R. This workaround allows us to move
forward while we investigate this problem.

Even with -fno-asynchronous-unwind-tables there are still two Rcpp
unit tests that crash on win64: test.Module.member and
test.Module.property. These tests segfault when an exception is raised
within a module. The problem still exists in the latest Rcpp version
from Github. It is unclear if this is related to the sjlj bug above,
or a separate problem in Rcpp / R-devel. The issue can be worked
around by changing Rcpp's Makevars.win to:

   PKG_CXXFLAGS=-mno-sse

With this fix, Rcpp is able to execute all unit tests on both win32
and win64. All tests pass, except for an issue with dates (also only
on win64) that is reported at [3].

[1] http://www.stat.ucla.edu/~jeroen/mingw-w64/
[2] http://www.stat.ucla.edu/~jeroen/mingw-w64/readme.txt
[3] https://github.com/RcppCore/Rcpp/issues/359