Add HUNTER_TOOLCHAIN_UNDETECTABLE_ID
Add HUNTER_TOOLCHAIN_UNDETECTABLE_ID

Add extra variable to toolchain-id calculation module so compiler flags that
are undetectable by C++ macro can affect toolchain-id.

Note: there is no macro to detect such flags but produced libraries are not the
same. I.e. `clang++ -fvisibility=default` and `clang++ -fvisibility=hidden`

isaachier/hunter,daminetreg/hunter,ledocc/hunter,vdsrd/hunter,dmpriso/hunter,NeroBurner/hunter,xsacha/hunter,ruslo/hunter,dan-42/hunter,xsacha/hunter,mchiasson/hunter,zhuhaow/hunter,ulricheck/hunter,dvirtz/hunter,lucmichalski/hunter,ikliashchou/hunter,x10mind/hunter,zhuhaow/hunter,isaachier/hunter,tatraian/hunter,ikliashchou/hunter,designerror/hunter,fwinnen/hunter,sumedhghaisas/hunter,madmongo1/hunter,headupinclouds/hunter,ikliashchou/hunter,ledocc/hunter,pretyman/hunter,sumedhghaisas/hunter,ingenue/hunter,isaachier/hunter,headupinclouds/hunter,caseymcc/hunter,tatraian/hunter,RomanYudintsev/hunter,xsacha/hunter,dvirtz/hunter,madmongo1/hunter,Knitschi/hunter,akalsi87/hunter,akalsi87/hunter,lucmichalski/hunter,ruslo/hunter,dan-42/hunter,caseymcc/hunter,jkhoogland/hunter,vdsrd/hunter,shekharhimanshu/hunter,RomanYudintsev/hunter,mchiasson/hunter,headupinclouds/hunter,pretyman/hunter,fire-hunter/hunter,dvirtz/hunter,ruslo/hunter,ingenue/hunter,ThomasFeher/hunter,madmongo1/hunter,alamaison/hunter,designerror/hunter,sumedhghaisas/hunter,Knitschi/hunter,ThomasFeher/hunter,pretyman/hunter,lucmichalski/hunter,dan-42/hunter,NeroBurner/hunter,stohrendorf/hunter,designerror/hunter,madmongo1/hunter,isaachier/hunter,jkhoogland/hunter,shekharhimanshu/hunter,tatraian/hunter,ErniBrown/hunter,xsacha/hunter,fire-hunter/hunter,jkhoogland/hunter,ingenue/hunter,ErniBrown/hunter,dmpriso/hunter,mchiasson/hunter,ingenue/hunter,dan-42/hunter,fire-hunter/hunter,stohrendorf/hunter,pretyman/hunter,ikliashchou/hunter,ErniBrown/hunter,x10mind/hunter,shekharhimanshu/hunter,vdsrd/hunter,daminetreg/hunter,ulricheck/hunter,ThomasFeher/hunter,ledocc/hunter,NeroBurner/hunter,stohrendorf/hunter,Knitschi/hunter,NeroBurner/hunter,caseymcc/hunter,akalsi87/hunter,alamaison/hunter,fwinnen/hunter,ErniBrown/hunter,zhuhaow/hunter,dmpriso/hunter,daminetreg/hunter,fwinnen/hunter,RomanYudintsev/hunter,ruslo/hunter,alamaison/hunter,ulricheck/hunter,x10mind/hunter,mchiasson/hunter