silver-searcher: updated to 0.19.2

[madjar]

Also fixed the "libgcc_s.so.1 must be installed for pthread_cancel to
work" problem.

[bjornfor]

Applied, thanks!

[pmahoney]

The -lgcc_s flag breaks compilation on Max OS X. gcc fails with

ld: library not found for -lgcc_s
collect2: error: ld returned 1 exit status

A possible fix is to do the same as libusb1, though a more general solution might be better...

For what it's worth, I built silver-searcher by removing the -lgcc_s flag, and otool -L result/bin/ag shows that it is linked to libgcc_s:

./result/bin/ag:
    /nix/store/l5a5n764xq98qv7rr67ymkm43ja45nx3-pcre-8.34/lib/libpcre.1.dylib (compatibility version 4.0.0, current version 4.2.0)
    /nix/store/3pl88z2fypvfmmz63dwnha9mfsrbcxyb-xz-5.0.5/lib/liblzma.5.dylib (compatibility version 6.0.0, current version 6.5.0)
    /nix/store/1vnmcd4rwbaiw1qxnk5gpm24cywql2y5-zlib-1.2.8/lib/libz.1.dylib (compatibility version 1.0.0, current version 1.2.8)
    /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 169.3.0)
    /nix/store/y03601mpyjv24psrgj6rigq99bkav2ip-gcc-4.8.2/lib/libgcc_s.1.dylib (compatibility version 1.0.0, current version 1.0.0)

[madjar]

Here is a PR with your proposed change: #1930.

By the way, don't hesitate to submit those kind of PR yourself. If you have a working darwin system, your input is infinitely more valuable than mine.