4-component parsing, and arm*-*-none-eabi in particular

[John Ericson]

Hello,

I've long noticed that configs like `armv7m-unknown-none-eabi`, though 
supported by LLVM, are not supported by gnu-config. [LLVM would treat 
"none" as the kernel, and "eabi" as the OS/ABI.] I recently found the 
time to go investigate why, and this is what I found and patched.

The problem is the way 4-component configs (i.e. 3 dashes) are parsed. 
Commit b7ab42761455e051a57876252740cb398aa952eb is the source of this 
support, which works by special-casing certain KERNEL-OPERATING_SYSTEM 
pairs, to disambiguate between CPU_TYPE-MANUFACTURER-OPERATING_SYSTEM 
and CPU_TYPE-KERNEL-OPERATING_SYSTEM.

This is fine for 3-component triples, but is overkill in the 4-component 
case where the config is always unambiguously 
CPU_TYPE-KERNEL-OPERATING_SYSTEM. Additionally, the original `if [ 
$basic_machine != $1 ]` check to disambiguate between 1- and 2-component 
configs is a bit obtuse.

I rewrote the whole chunk of code in what I hope you all agree is a more 
readable manner, using sed only to pull out the (up to 4) components and 
then doing everything else with simple pure bash. Finally, I whitelisted 
and tested `arm*-*-none-eabi`, which I hope a conservative starting point.

Hopefully this all makes sense, and the commit messages add additional 
clarity.

Thanks,

John

0001-Rewrite-basic_machine-if-with-case.patch
Description: Text document

0002-Rewrite-logic-handling-n-separated-components.patch
Description: Text document

0003-Accept-arm-none-eabi.patch
Description: Text document