ICU-23357 measunit_extra.cpp: Fix error: 'abs' ambiguous #5161

Job	Run time
clang-valgrind-intltest (collator)	5m 40s
clang-valgrind-test	10m 21s
clang-valgrind-intltest (rbnfrt)	7m 5s
clang-valgrind-intltest (rbnf)	6m 31s
clang-valgrind-intltest (icuserv)	5m 50s
clang-valgrind-intltest (rbnfp)	5m 5s
clang-valgrind-intltest (rbbi)	9m 46s
clang-valgrind-intltest (normalize)	6m 47s
clang-valgrind-intltest (csdet)	5m 42s
clang-valgrind-intltest (idna)	6m 33s
clang-valgrind-intltest (utility)	7m 4s
clang-valgrind-intltest (translit)	6m 37s
clang-valgrind-intltest (convert)	7m 9s
clang-valgrind-intltest (bidi)	6m 17s
clang-valgrind-intltest (spoof)	5m 55s
clang-valgrind-intltest (regex)	6m 26s
clang-valgrind-intltest (format)	17m 16s
	2h 6m 4s

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