Bug 1316540 - Update version requirement for --with-system-icu to 58.1 for Unicode 9 support. r=waldo

build/autoconf/icu.m4

@@ -15,7 +15,7 @@ MOZ_ARG_WITH_BOOL(system-icu,
     MOZ_SYSTEM_ICU=1)
 
 if test -n "$MOZ_SYSTEM_ICU"; then
-    PKG_CHECK_MODULES(MOZ_ICU, icu-i18n >= 50.1)
+    PKG_CHECK_MODULES(MOZ_ICU, icu-i18n >= 58.1)
     CFLAGS="$CFLAGS $MOZ_ICU_CFLAGS"
     CXXFLAGS="$CXXFLAGS $MOZ_ICU_CFLAGS"
 fi