Do not explicitly report "standard" include directories as implicit

In commit 1293ed85 (ParseImplicitIncludeInfo: keep implicit incl.
consistent when rerunning cmake, 2019-01-30, v3.14.0-rc1~26^2) we did
not account for `CMAKE_<LANG>_STANDARD_INCLUDE_DIRECTORIES`.  This
variable lets platform modules or toolchain files specify directories
that are to be explicitly passed as standard include directories.  These
include directories are used by the test project from which we extract
implicit include directories so they appear in the parsed results
whether or not the compiler really considers them implicit.  Exclude
these entries from the computed implicit include directories since they
are not actually implied by the compiler when we invoke it with
"standard" include directories passed explicitly.

Instead teach the build system generators to treat the "standard"
directories as implicit for purposes of excluding them from appearing
earlier in the compiler command line due to `include_directories` and
`target_include_directories` calls.

Issue: #18936, #18944
36 jobs for fix-legacy-implicit-includes
Status Job ID Name Coverage
  External
passed cdash

passed cmake-dash3win7-windows-release-ninja

passed cmake-minoc-linux-release-lint-iwyu-tidy

passed cmake-moonshade-osx-debug-ninja

passed cmake-moonshade-osx-release-makefiles

passed cmake-terfin-windows-release-vs2017

passed ghostflow-check-master

passed ghostflow-stager

passed cmake-dash3win7-windows-release-ninja

passed cmake-dash3win7-windows-release-ninja

00:30:33

passed cmake-dash3win7-windows-release-ninja

passed cmake-dash3win7-windows-release-ninja

passed cmake-minoc-linux-release-lint-iwyu-tidy

00:11:44

passed cmake-minoc-linux-release-lint-iwyu-tidy

passed cmake-minoc-linux-release-lint-iwyu-tidy

passed cmake-minoc-linux-release-lint-iwyu-tidy

passed cmake-moonshade-osx-debug-ninja

passed cmake-moonshade-osx-debug-ninja

passed cmake-moonshade-osx-debug-ninja

00:11:56

passed cmake-moonshade-osx-debug-ninja

passed cmake-moonshade-osx-release-makefiles

passed cmake-moonshade-osx-release-makefiles

passed cmake-moonshade-osx-release-makefiles

00:14:25

passed cmake-moonshade-osx-release-makefiles

passed cmake-terfin-windows-release-vs2017

passed cmake-terfin-windows-release-vs2017

00:49:06

passed cmake-terfin-windows-release-vs2017

passed cmake-terfin-windows-release-vs2017

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager

passed ghostflow-stager