I don't think there's a built in way to do this, we modified the cotire function cotire_add_pch_compilation_flags (line 1244 cotire.cmake version 1.5.1) to add the "-w" flag when compiling the precompiled header. We changed the GNU|CLang section to read
elseif (_compilerID MATCHES "GNU|Clang")
# GCC / Clang options used
# -x specify the source language
# -c compile but do not link
# -o place output in file
set (_xLanguage_C "c-header")
set (_xLanguage_CXX "c++-header")
if (_flags)
# append to list
list (APPEND _flags "-x" "${_xLanguage_${_language}}" "-w" "-c" "${_prefixFile}" -o "${_pchFile}")
else()
# return as a flag string
set (_flags "-x ${_xLanguage_${_language}} -w -c \"${_prefixFile}\" -o \"${_pchFile}\"")
endif()
This suppresses all warnings for us, we have a lot of warnings turned on - including -Werror, so it was an essential change!