- Template gcc-go.patch to substitute gcc_go_version and eliminate
multiple similar patches each with hardcoded gcc go binary name.
gcc-go.patch inserts gcc-go binary name e.g. go-8 to compensate
for current lack of gcc-go update-alternatives usage.
* add gcc-go.patch
* drop gcc6-go.patch
* drop gcc7-go.patch

- For SLE-12 set gcc_go_version to 8 to bootstrap using gcc8-go.
gcc6-go and gcc7-go no longer successfully bootstrap go1.17 or
go1.18 on SLE-12 aarch64 ppc64le or s390x.
* gcc6-go fails with errors e.g. libnoder.a(_go_.o):(.toc+0x0):
undefined reference to `__go_pimt__I4_DiagFrN4_boolee3 (forwarded request 967627 from jfkw)