[Clang] avoid relying on StringMap iteration order when roundtripping -analyzer-config

I am working on another patch that changes StringMap's hash function,
which changes the iteration order here, and breaks some tests,
specifically:

    clang/test/Analysis/NSString.m
    clang/test/Analysis/shallow-mode.m

with errors like:

    generated arguments do not match in round-trip
    generated arguments #1 in round-trip: <...> "-analyzer-config" "ipa=inlining" "-analyzer-config" "max-nodes=75000" <...>
    generated arguments #2 in round-trip: <...> "-analyzer-config" "max-nodes=75000" "-analyzer-config" "ipa=inlining" <...>

To avoid this, sort the options by key, instead of using the default map
iteration order.

Reviewed By: jansvoboda11, MaskRay

Differential Revision: https://reviews.llvm.org/D142861