Do not use -mdynamic-no-pic on Darwin

Latest OS X versions ignore this flag as non PIC objects are
discouraged.
Properly mark Uint literals as unsigned in big.c
Properly declare _sigaction on Darwin
Define matherr only on platforms where it is used
Fix two deprecation warnings in com.ericsson.otp.ic.Environment
Fix a shift/reduce conflicts warning in icparse
Fix some sign warnings found with Clang
Merge branch 'nox/fix-warnings/OTP-11086' into maint

* nox/fix-warnings/OTP-11086:
  Fix some sign warnings found with Clang
  Fix a shift/reduce conflicts warning in icparse
  Fix two deprecation warnings in com.ericsson.otp.ic.Environment
  Define matherr only on platforms where it is used
  Properly declare _sigaction on Darwin
  Properly mark Uint literals as unsigned in big.c
  Do not use -mdynamic-no-pic on Darwin