build: prereq: tidy gcc version checks

build: prereq: tidy gcc version checks

There is a restriction in the number of parameters(10)  that may be passed to
the SetupHostCommand macro so continually adding explicit gcc'n' version
checks ends up breaking the compiler check for the later versions and
oddballs like Darwin as was done in 835d1c68a0 which added gcc10.

Drop all the explicitly specified gcc version checks.  If a suitable gcc
compiler is not found, it may be specified at the dependency checking
stage after which that version will be symlinked into the build staging
host directory.

eg. 'CC=gccfoo CXX=g++foo make prereq'

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>
Acked-by: Jo-Philipp Wich <jo@mein.io>