Sort list of source files

[reinerh]

$(wildcard) does not guarantee a sorted list, which causes
also a non-deterministic order while linking the binary.
To support reproducible building, the list is explicitely sorted.

[bcopeland]

I'd like to take this patch and support reproducible building in general, but please note:

• I need a signed-off-by to apply (see CONTRIBUTING)
• There's a pending branch to convert everything to cmake. I presume something like this would still beuseful there though.

[reinerh]

Just amended the commit with a signed-off-by.

For cmake probably no further change is required.
I see that you are using file(GLOB ...) there, which could be sorted with list(SORT ...), but a patch for cmake is already pending (not sure if it's released yet), which guarantees a sorted order in file(GLOB ...), see:
https://cmake.org/gitweb?p=cmake.git;a=commitdiff;h=edcccde7

[bcopeland]

Thanks - any other patches needed for reproducible builds are more than welcome.