Linux: Mismatch with gcc being used on clang builds

[m-fol]

When attempting to build Boost on a Linux system, this will default to TOOLSET=gcc, regardless if it's a Clang build or not:

lcg.bits/boost.sh

Lines 28 to 32 in 5fca963

	function Make() {
	case $(uname) in
	Darwin) TOOLSET=clang ;;
	*) TOOLSET=gcc ;;
	esac

Log:

2026-07-21@15:25:08:DEBUG:Boost:Boost:1.90.0: + ./bootstrap.sh --with-toolset=gcc 
--with-python=/builds/zWVH0Cj2o/0/sft/stacks/bits/lcg.bits-empty/lcg.bits/x86_64-el9-clang16-dbg/Python/3.13.11-local1/bin/python3 
--with-python-root=/builds/zWVH0Cj2o/0/sft/stacks/bits/lcg.bits-empty/lcg.bits/x86_64-el9-clang16-dbg/Python/3.13.11-local1