[tlbuild] Static linking of C++ runtime library causing problems on x86_64-cygwin

[Ken Brown]

Hi Peter,

Several years ago you came up with a way of statically linking the C++ 
runtime library on Cygwin, which you incorporated into kpse-cxx-hack.m4. 
  It turns out that this is causing problems for the build of TeX Live 
on x86_64-cygwin.  [The same problem should actually occur on 
x86-cygwin, but it currently doesn't because of a minor packaging 
difference between the x86 and x86_64 distributions.  This will change 
in the future.]

Specifically, the link command line for xetex looks like this:

   g++...-o xetex.exe...-lfontconfig -lexpat -lfreetype...-static...

and the -static flag causes the linker to try to statically link 
fontconfig, expat, and freetype.  This fails because Cygwin doesn't have 
static libraries for fontconfig and freetype.  (It does have one for 
expat, but this may change in the future.)

A fix would be to change the library flags to

   -Wl,-Bdynamic -lfontconfig -lexpat -lfreetype -Wl,-Bstatic

Is this easy to accomplish?  If not, maybe we should just give up 
statically linking the C++ library on Cygwin, unless you think that's 
important.

Thanks.

Ken