test_identifierTypesFromSpecialIdentifier() fails on Darwin (swiftlang#333)

This is caused by ICU's update: rdar://114361374.

Introduce FIXED_ICU_20187 to indicate the ICU version with the fix and update test expectation behind the flag. The upstream change unicode-org/icu@1afef30 is scheduled to go into ICU 74. Darwin ICU picked this up earlier than their annual ICU update. When we update FoundationICU to ICU74 we should remove this flag and enable the desired behavior everywhere.

Resolves rdar://118564689

Author: itingliu

Tests/FoundationInternationalizationTests/LocaleTests.swift

@@ -161,9 +161,15 @@ final class LocaleTests : XCTestCase {
             return localeComponents
         }
 
+#if FIXED_ICU_20187
+        verify(cldr: "root", bcp47: "und", icu: "") {
+            return Locale.Components(identifier: "")
+        }
+#else
         verify(cldr: "root", bcp47: "und", icu: "en_US_POSIX") {
             return Locale.Components(identifier: "")
         }
+#endif
 
         verify(cldr: "und_US", bcp47: "und-US", icu: "_US") {
             return Locale.Components(languageRegion: .unitedStates)
@@ -753,7 +759,11 @@ extension LocaleTests {
 
     // TODO: Reenable once (Locale.canonicalIdentifier) is implemented
     func test_identifierTypesFromSpecialIdentifier() throws {
+#if FIXED_ICU_20187
+        verify("", cldr: "root", bcp47: "und", icu: "")
+#else
         verify("", cldr: "root", bcp47: "und", icu: "en_US_POSIX")
+#endif
         verify("root", cldr: "root", bcp47: "root", icu: "root")
         verify("und", cldr: "root", bcp47: "und", icu: "und")
 
@@ -772,12 +782,20 @@ extension LocaleTests {
 
         // If there's only one component, it is treated as the language code
         verify("123", cldr: "root", bcp47: "und", icu: "123")
+#if FIXED_ICU_20187
+        verify("😀123", cldr: "root", bcp47: "und", icu: "")
+#else
         verify("😀123", cldr: "root", bcp47: "und", icu: "en_US_POSIX")
+#endif
 
         // The "_" prefix marks the start of the region
         verify("_ZZ", cldr: "und_ZZ", bcp47: "und-ZZ", icu: "_ZZ")
         verify("_123", cldr: "und_123", bcp47: "und-123", icu: "_123")
+#if FIXED_ICU_20187
+        verify("_😀123", cldr: "root", bcp47: "und", icu: "")
+#else
         verify("_😀123", cldr: "root", bcp47: "und", icu: "en_US_POSIX")
+#endif
 
         // Starting an ID with script code is an acceptable special case
         verify("Hant", cldr: "hant", bcp47: "hant", icu: "hant")