ICU-23357 measunit_extra.cpp: Fix error: 'abs' ambiguous #5160

Job	Run time
clang-valgrind-test	10m 28s
clang-valgrind-intltest (collator)	6m 3s
clang-valgrind-intltest (regex)	5m 27s
clang-valgrind-intltest (translit)	7m 4s
clang-valgrind-intltest (rbbi)	9m 55s
clang-valgrind-intltest (utility)	7m 29s
clang-valgrind-intltest (normalize)	6m 38s
clang-valgrind-intltest (rbnfrt)	37m 16s
clang-valgrind-intltest (icuserv)	5m 22s
clang-valgrind-intltest (rbnf)	7m 12s
clang-valgrind-intltest (spoof)	5m 34s
clang-valgrind-intltest (csdet)	5m 39s
clang-valgrind-intltest (format)	16m 42s
clang-valgrind-intltest (convert)	6m 22s
clang-valgrind-intltest (idna)	6m 30s
clang-valgrind-intltest (bidi)	5m 59s
clang-valgrind-intltest (rbnfp)	5m 49s
	2h 35m 29s

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