BLD: preserve library order

[nolta]

Before, the list of libraries was resorted to match the order of library_dirs. Now, the opposite occurs: library_dirs is resorted to match the library order.

Ran into this problem while trying to build numpy for a Bluegene/Q. The order static libraries are passed to the linker is important.

[rgommers]

CI failed: https://travis-ci.org/numpy/numpy/jobs/134270630. The error looks related to this PR, somehow ATLAS went missing. It only failed because of compiling with -OO, but ATLAS should be found during the build.

[rgommers]

@nolta it would also be useful to provide the relevant part of the build log for your failing build. Both for searchability for the next person that runs into the issue you found, and for us to understand better what is going wrong here.

[nolta]

Basically, i have 2 directories and 3 libraries, and i need to make a library sandwich:

library_dirs = X : Y
libs = a, b, c

Libraries a and c are in directory X while library b is in Y.

The library order a, b, c is important. However, numpy reorders the libraries to match the directories. So only

library_dirs = X : Y
libs = a, c, b

or

library_dirs = Y : X
libs = b, a, c

are currently allowed.

[nolta]

CI now green. Was missing a break statement.

[charris]

@rgommers LGTY?

[charris]

Needs a comment in the code so it doesn't get "cleaned up" later. Also a comment in the release notes.

[charris]

@rgommers This seems like a reasonable change to me.

[nolta]

Added a comment & release note.

[charris]

Why not leave this part? It is a bit confusing to do it after breaking from the loop.

[nolta]

Not sure i understand? This change is almost entirely whitespace: c84c875?w=1

[charris]

Thanks @nolta .