Use compiler intrinsic functions for signed integer math when overflow

detection is needed.

FossilOrigin-Name: d3ac32a6e7f1823450feb3d1089802542090d164

diff --cc manifest
index cff39d7dca9a4d339484cd041f843df976455258,b1dbc792e4c24c880d19ec77929df888c421c750..c7180b283185940e6327448d61fcdddf7030de5e
--- 1/manifest
--- 2/manifest
+++ b/manifest
@@@ -1,5 -1,5 +1,5 @@@
- C Add\sthe\sexperimental\saffinity()\sSQL\sfunction\swhen\sSQLITE_DEBUG\sis\sdefined.
- D 2017-01-03T14:45:35.313
 -C Back\sout\sthe\suse\sof\s__sync_fetch_and_sub()\sas\sit\sdoes\snot\sappear\sto\swork.
 -D 2017-01-03T21:50:49.166
++C Use\scompiler\sintrinsic\sfunctions\sfor\ssigned\sinteger\smath\swhen\soverflow\ndetection\sis\sneeded.
++D 2017-01-03T21:57:11.355
  F Makefile.in 41bd4cad981487345c4a84081074bcdb876e4b2e
  F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
  F Makefile.msc b8ca53350ae545e3562403d5da2a69cec79308da
@@@ -1541,8 -1541,8 +1541,8 @@@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a9
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  U drh
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++Z 6bd6e679c9840443d9b2f38c8bc4573f

diff --cc manifest.uuid
index 1ef467555f5d6110b10659a93cb8e11803c19810,2a6301b72a731784b7d081952314f7299dd86374..42e6e71ba8205dfe913a11cbdaf4132b14771a79
--- 1/manifest.uuid
--- 2/manifest.uuid
+++ b/manifest.uuid
@@@ -1,1 -1,1 +1,1 @@@
- bed0eaa5f50112e64fc97a2afdc9d56cf8f5026a
 -4c2efd4239bf07eb4b92d4af54edd68ee6312670
++d3ac32a6e7f1823450feb3d1089802542090d164