Commits on Sep 13, 2019

1. Clean up + fix build scripts re: USE_SSE= and PORTABLE= …

   Summary: In preparing to utilize a new Intel instruction extension, I
   noticed problems with the existing build script in regard to the
   existing utilized extensions, either with USE_SSE or PORTABLE flags.
   
   * PORTABLE=0 was interpreted the same as PORTABLE=1. Now empty and 0
   mean the same. (I guess you were not supposed to set PORTABLE= if you
   wanted non-portable--except that...)
   * The Facebook build script extensions would set PORTABLE=1 even if
   it's already set in a make var or environment. Now it does not override
   a non-empty setting, so use PORTABLE=0 for fully optimized build,
   overriding Facebook environment default.
   * Put in an explanation of the USE_SSE flag where it's used by
   build_detect_platform, and cleaned up some confusing/redundant
   associated logic.
   * If USE_SSE was set and expected intrinsics were not available,
   build_detect_platform would exit early but build would proceed with
   broken, incomplete configuration. Now warning is gracefully recovered.
   * If USE_SSE was set and expected intrinsics were not available,
   build would still try to use flags like -msse4.2 etc. which could lead
   to unexpected compilation failure or binary incompatibility. Now those
   flags are not used if the warning is issued.
   
   Test Plan: manual case testing

   

   pdillinger committed Sep 13, 2019
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