more helpful error message for 32/64 bit dll mismatch on windows

[mlubin]

Something that caught me today, and I imagine will catch a large number of users in the future, is trying to open a 32-bit dll from win64 julia. This is something that there should be a more useful error message for. The discussion at http://stackoverflow.com/questions/495244/how-can-i-test-a-windows-dll-to-determine-if-it-is-32bit-or-64bit seems to indicate that it's possible but a bit messy.

[vtjnash]

It would be nice, but we don't really know why windows failed to open a dll, or even which dll's it tried to open. We could only attempt to guess.

I think we should just replace window's generic and meaningless %1 is not a valid win32 application with a custom message which suggests various fixes: dll could not be found in Base.LD_LOAD_PATH, the current directory, or %PATH%; it has failed dependencies; or it was not a valid win$WORD_SIZE binary

[mlubin]

Well 32/64 bit is something I believe could be explicitly checked before even trying to open the dll. I'll leave it up to you to decide if it's worth the trouble.

[vtjnash]

my point is that we never open the dll. we just ask windows to search for the first dll it can load. trying to emulate the linker is possible, but generally not advisable. replacing the error message, however, is very straightforward and would be equally (or more?) helpful.

[mlubin]

I see the issue. Changing the error message will definitely be an improvement.

[staticfloat]

@vtjnash; not disagreeing with you, but we do already emulate an incredible amount of the dynamic linker on OSX and Linux. We search path lists, cache library name -> path mappings, etc... ;)

[ihnorton]

Breadcrumb: #7940