Makefile: Fix per-config linker PDB output directory

Also, now that all call sites of cmTarget::GetPDBName and
cmTarget::GetPDBDirectory pass the configuration, make the
argument non-optional.
Help: Refactor PDB_NAME and PDB_OUTPUT_DIRECTORY docs

Move the note about VS 6 into the PDB_NOTE.txt common include file
and include it from the per-config properties too.  Also re-word
the note to clarify the separate compiler and linker flags involved
and state explicitly that compiler flags are not affected.
MSVC: Add properties to configure compiler PDB files (#14762)

Since commit v2.8.12~437^2~2 (VS: Separate compiler and linker PDB files
2013-04-05) we no longer set /Fd with the PDB_NAME or PDB_OUTPUT_DIRECTORY
properties.  Those properties now exclusively handle linker PDB files.
Since STATIC libraries do not link their compiler PDB file becomes more
important.  Add new target properties "COMPILE_PDB_NAME[_<CONFIG>]" and
"COMPILE_PDB_OUTPUT_DIRECTORY[_<CONFIG>]" to specify the compiler PDB
file location and pass the value to the MSVC /Fd option.
Merge topic 'msvc-compiler-pdb-files' into next

730e6d7d MSVC: Add properties to configure compiler PDB files (#14762)
7aa55bdc Help: Refactor PDB_NAME and PDB_OUTPUT_DIRECTORY docs
e94f3226 Makefile: Fix per-config linker PDB output directory