Stop signed left shift overflows in curve25519-donna (non-64-bit)
Similarly to #13280 (moved), the curve25519-donna.c code contains some signed left shifts of negative numbers, which clang identifies as runtime errors. (This is only an issue with the generic code, not the 64-bit code.)
Under -ftrapv, this causes a trap/crash.
I've used a similar strategy to the one in #13280 (moved), where we automate the entire SHL32/SHL64 conversion using a perl script. The first commit sets up the macros.
The safe SHL32/SHL64 macros perform potentially overflowing left shifts in unsigned arithmetic.
I'll post a branch as soon as I've set up a change entry (for which I need the bug number).
Version: tor 2.6.?-alpha git: fc5cab44724e8328e2186f22114625388f1c8f0d (Thu Oct 16 13:29:14 2014 -0400)
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