Usage of `-fno-pch-timestamp` breaks clang builds on macOS 10.7–10.11

[barracuda156]

Build log: https://build.macports.org/builders/ports-10.11_x86_64-builder/builds/271191/steps/install-port/logs/stdio

The problem is created by this chunk of code:

LucenePlusPlus/cmake/cotire.cmake

Lines 1673 to 1694 in 76dc90f

	elseif (_compilerID MATCHES "Clang")
	if (UNIX)
	# Clang options used
	# -x specify the source language
	# -c compile but do not link
	# -o place output in file
	# -fno-pch-timestamp disable inclusion of timestamp in precompiled headers (clang 4.0.0+)
	set (_xLanguage_C "c-header")
	set (_xLanguage_CXX "c++-header")
	if (_flags)
	# append to list
	list (APPEND _flags -x "${_xLanguage_${_language}}" -c "${_prefixFile}" -o "${_pchFile}")
	if (NOT "${_compilerVersion}" VERSION_LESS "4.0.0")
	list (APPEND _flags -Xclang -fno-pch-timestamp)
	endif()
	else()
	# return as a flag string
	set (_flags "-x ${_xLanguage_${_language}} -c \"${_prefixFile}\" -o \"${_pchFile}\"")
	if (NOT "${_compilerVersion}" VERSION_LESS "4.0.0")
	set (_flags "${_flags} -Xclang -fno-pch-timestamp")
	endif()
	endif()

Apparently Clang version threshold is wrong.