[bug-gawk] Invalid result when converting to hex literal

[Steven Penny]

Tested with Gawk 4.2.1 and 4.1.4. Hex literals work as expected:

   $ awk 'BEGIN {print 0x21}'
   33

   $ awk --posix 'BEGIN {print 0x21}'
   0

However when converting from string to hex literal, you get the opposite of what
is supposed to happen:

   $ awk 'BEGIN {print +"0x21"}'
   0

   $ awk --posix 'BEGIN {print +"0x21"}'
   33

in all examples, you should be getting "33" when not using POSIX. Note that all
Mawk versions work as expected.