CMakeDetermine*Compiler: Remove temporary cache entry

When the user or toolchain file sets CMAKE_<LANG>_COMPILER to a name
without a path we use find_program with CMAKE_<LANG>_COMPILER_WITH_PATH
to search for the tool.  Remove the temporary cache entry afterward to
avoid exposing it to projects.  It is not set by other logic paths so no
one should be using it.
Ninja: use deps = gcc/msvc feature

cmcldeps is now only used for .rc file processing
Tests: use string(TIMESTAMP) instead of system and locale specific date/time
CTest: restore old failed test priority in serial test runs
CMakeDetermineCompilerId: Always use compiler detected from IDE

When compiler id detection also provides a CMAKE_<LANG>_COMPILER
value, use it unconditionally.  It is known to be the compiler
that is actually in use by IDE builds in VS and Xcode.  Do not
let a stray cache entry try to say otherwise.
Require CMAKE_<LANG>_COMPILER to be found as a full path

All generators now support detection of the full path to the compiler, so
require it to be so.  This will allow CMake<LANG>Information.cmake and
other logic to assume the full path to the compiler tool is available.

The Makefile generators already rejected CMAKE_<LANG>_COMPILER values
that did not name an existing compiler.  Extend this error message to
all generators, make it occur as early as possible, and improve the
message with advice about how to set the compiler.  If the full path to
the compiler is not known, finish enabling languages with a fatal error
so configuration does not continue.

For now, allow the RC language compiler to not be a full path.  Later we
will need to detect the full path to "rc" under the VS IDE.

Add a RunCMake.CompilerNotFound test to cover failure cases.
Fix the RunCMake.CompilerChange test EmptyCompiler case to work
when configuration does not continue past enable_language.
Merge topic 'ninja-use-deps'

eeb4aec Ninja: use deps = gcc/msvc feature
Merge topic 'locale-independent-date-in-test'

0655d09 Tests: use string(TIMESTAMP) instead of system and locale specific date/time
Merge topic 'restore-serial-failed-test-order'

2b5c9da CTest: restore old failed test priority in serial test runs
Merge topic 'enable-language-require-compiler'

3e04946 Require CMAKE_<LANG>_COMPILER to be found as a full path
6007f7c CMakeDetermineCompilerId: Always use compiler detected from IDE
332771c CMakeDetermine*Compiler: Remove temporary cache entry