[PATCH] Makefile: Fix POSIX grep alternation regex

[Andreas Schwab]

On Nov 11 2024, Igor Melnikov wrote:

> Using grep -E for extended regular expression syntax with non-escaped
> alternation operator | lets both versions interpret the pattern
>  unambiguously and the check to function properly on systems with POSIX
>  grep as well.

Alternatively, you can use multiple -e options.  This works even with
traditional grep implementations.

-- 
Andreas Schwab, schwab at linux-m68k.org
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