Explicitly qualify ICU types with icu:: namespace

It will be required by ICU 61 anyway, see
https://ssl.icu-project.org/repos/icu/trunk/icu4c/readme.html#RecBuild

Change-Id: Ib7accd75a6e35932048d779cf7bf0a5a33f8ed0d
Reviewed-on: https://gerrit.libreoffice.org/46741Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>
(cherry picked from commit 8960ecc6)
Reviewed-on: https://gerrit.libreoffice.org/56680
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
(cherry picked from commit 8790243d)

opencl/source/openclconfig.cxx

@@ -119,7 +119,7 @@ bool match(const OUString& rPattern, const OUString& rInput)
     UErrorCode nIcuError(U_ZERO_ERROR);
     icu::UnicodeString sIcuPattern(reinterpret_cast<const UChar*>(rPattern.getStr()), rPattern.getLength());
     icu::UnicodeString sIcuInput(reinterpret_cast<const UChar*>(rInput.getStr()), rInput.getLength());
-    RegexMatcher aMatcher(sIcuPattern, sIcuInput, 0, nIcuError);
+    icu::RegexMatcher aMatcher(sIcuPattern, sIcuInput, 0, nIcuError);
 
     return U_SUCCESS(nIcuError) && aMatcher.matches(nIcuError) && U_SUCCESS(nIcuError);
 }