Adding logic to undef IOP_MODEL before we include the env that may define it, that way the ENV can't be setting it

Makefiles now honor symvers file locations if they are already specified in the environment.
This could cause problems if variables are unkowingly left defined.
A better option would be to override the variables on the command line
Variable names are changed to make it easier to derive them from module names.

Setting epics/util/Makefile.in to custom output dir and regenerating configure script for it, don't copy files that can cause race condition

 * Remove the possibility to have variable string lengths passed in.
 * Work with an out parameter that knows its size and can assert it to the caller.

 * Adjust function to not modify its input (const safe)
 * Switch append operation to direct assignment instead of strncat which was overflowing the destination buffers due to improper usage.
   * could do a bsd style strlcat, but we explicitly check the length right above it.

 * Fix how lines with leading quotes are handled, they are treated as quotes, not as normal characters now.
 * Properly terminate a long quoted string that would overflow an output.
   * Note this is not complete, it still writes one character past where it should.

 * Change the data type union to use a fixed_string<64> instead of char[64].
   * With accompanying simplifications around string assignment.