build_visit improvements for patching

[markcmiller86]

Proposed best practices for handling patching in build_visit

• Only use patch -p0 << \EOF not a bare EOF without the leading backslash.
  • Rationale: \EOF is necessary to patch code involving $ chars (e.g. shell code)
• Maximally restrict patching so that patches are applied under only the conditions we have verified they are necessary. For example, if a package builds fine everywhere except macOS, ensure the patch is restricted to macOS.
  • Rationale: should be self-evident...helps to minimize non-standard builds
• Put unrelated patches in different bash functions
• Name patch functions by package's version number and purpose (e.g. apply_cgns_410_missing_ldflags_patch)
  • Rationale: A given version of a TPL can require multiple patches to fix different issues
• Put logic effecting when a patch is applied in callers of the patch functions and not the patch functions themselves
  • Rationale: makes it a bit clearer to understand when patches get applied
• Use unified diff format for diffs used in patches (e.g. diff -u)
  • Rationale: Unified diffs are quite a bit shorter
• Put messaging related to patching in the patch functions and not the callers of those functions
  • Rationale: encpasulation
• Invoke patches after cd'ing to build dir
  • Rationale: ensures some level of consistency of how patches get defined
• Define patches relative to the build dir of the package
  • What about out of source builds?
• When libs are updated, old patch logic should be removed
  • Rationale: should be self-evident. When we bump the version of a lib, we no longer need to maintain patches for the older version.
• Conditional patching logic should not be predicated on compiler names and/or versions (see Patch application logic should not predicate on compiler name #19693)

The above would help to unify build_visit where patching is concerned.

[brugger1]

Before removing a patch, we should make sure it is no longer needed. We've had several instances of patches being removed that were fixing bugs rather than compile issues that caused non-obvious bugs to reappear.