[libclc] Enable DEPENDS_EXPLICIT_ONLY if cmake version >= 3.27

[wenju-he]

Commit 0c21d6b fixed sequential build of libclc on Windows by adding a target for each compile command.
This PR conditionally enables DEPENDS_EXPLICIT_ONLY and requires at least cmake version 3.27. DEPENDS_EXPLICIT_ONLY avoids adding too many targets.

[wenju-he]

sorry, DEPENDS_EXPLICIT_ONLY only works for Ninja generator, see https://cmake.org/cmake/help/latest/command/add_custom_command.html#command:add_custom_command
The main issue of sequential compilation we was is related to MSVC generator.
So the comments at

llvm-project/libclc/cmake/modules/AddLibclc.cmake

Lines 68 to 72 in a450dc8

	# FIXME: The target is added to ensure the parallel build of source files.
	# However, this may result in a large number of targets.
	# Starting with CMake 3.27, DEPENDS_EXPLICIT_ONLY can be used with
	# add_custom_command to enable parallel build.
	# Refer to https://gitlab.kitware.com/cmake/cmake/-/issues/17097 for details.

is probably unrelated to the issue that 0c21d6b addressed.
Close this PR. I'll fix the comment in another PR.