scripts/min-tool-version.sh: Raise minimum clang version to 18.0.0 for loongarch

The existing mainline clang development version encounters difficulties
compiling the LoongArch kernel module. It is anticipated that this issue
will be resolved in the upcoming 18.0.0 release. To prevent user
confusion arising from broken builds, it is advisable to raise the
minimum required clang version for LoongArch to 18.0.0.

Suggested-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/1941
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: WANG Rui <wangrui@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>