Details:
- Updated common.mk so that when --disable-shared option is given to
  configure:
  1. The -fPIC compiler flag is omitted from the individual 
     configuration family members' CPICFLAGS variables (which are 
     initialized in each subconfig's make_defs.mk file); and
  2. The BUILD_SYMFLAGS variable, which contains compiler flags needed 
     to control the symbol export behavior, is left blank.
- The net result of these changes is that flags specific to shared
  library builds are only used when a shared library is actually 
  scheduled to be built. Thanks to Nick Knight for reporting this issue.
- CREDITS file update.

Sanity check if I can trigger CI the same as Field