Integrate command-line parsing with fmv-afmv collision detection

[mfunkel]

What has been done?

• updated the collision detection and error production to integrate with the branch handling command-line parsing
• updated gcc/opts.cc to remove any references to afmv_cnt and afmv_targets variables, as those were causing issues when building
  • note: the variables are inaccessible across compilation units, and simply not using them would blow up the build with the warning about variables being set but unused - hence the removal
• updated gcc/multiple-target.cc to use command-line macro from "2024-S-command-line-parsing" branch
  • note: the name for this macro is misleading as it suggests the value is boolean when it actually would be a string (the name chosen by the command-line parsing branch developer is flag_fafmv which is poorly chosen and should be updated before making a submission to gcc)
  • the location of the command-line option within the larger context of the rest of the common.opt file is also oddly chosen, and should be moved to a more appropriate spot before making a submission to gcc
  • ideally, the variable afmv_cnt should be used to check for collision, but since that branch produces errors, we had to work around it by simply going off of the command-line macro instead

Usage

• build/install this version of gcc, and use it to compile a program that uses FMV on at least one function (i.e., __attribute__((target_clones("default","sve","sha2"))) )
• ensure that the afmv command-line option is set when compiling, ex. -fafmv="sve"
  • note: the command-line parsing branch currently only validates for simd, neon, sve, and sve2
• should notice the collision error being thrown with info regarding the problem and how to fix it