ICU-23357 measunit_extra.cpp: Fix error: 'abs' ambiguous #5151

Job	Run time
clang-valgrind-test	2m 41s
clang-valgrind-intltest (utility)	2m 18s
clang-valgrind-intltest (collator)	2m 26s
clang-valgrind-intltest (rbbi)	2m 11s
clang-valgrind-intltest (rbnf)	2m 41s
clang-valgrind-intltest (rbnfrt)	2m 44s
clang-valgrind-intltest (idna)	2m 48s
clang-valgrind-intltest (translit)	2m 22s
clang-valgrind-intltest (regex)	2m 47s
clang-valgrind-intltest (format)	2m 35s
clang-valgrind-intltest (spoof)	2m 28s
clang-valgrind-intltest (normalize)	2m 39s
clang-valgrind-intltest (icuserv)	2m 45s
clang-valgrind-intltest (convert)	2m 43s
clang-valgrind-intltest (bidi)	19m 29s
clang-valgrind-intltest (csdet)	2m 3s
clang-valgrind-intltest (rbnfp)	2m 39s
	1h 0m 19s

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