Expose ubrk_clone() from NDK - part 2

tools/icu4c_srcgen/libicu_export.txt is the only manual change,
and other file changes are generated by the script
tools/icu4c_srcgen/generate_ndk.py

CTS of ubrk_clone() should be covered in CtsIcu4cTestCases.
The test is TestBreakIteratorClone() located at
icu4c/source/test/cintltst/cbiapts.c

Bug: 177225118
Test: atest CtsIcu4cTestCases
Change-Id: I71f2eb80d99dc446a105d8733a791b85fb360898
diff --git a/libicu/libicu.map.txt b/libicu/libicu.map.txt
index 6603317..e47801e 100644
--- a/libicu/libicu.map.txt
+++ b/libicu/libicu.map.txt
@@ -165,6 +165,7 @@
     ubidi_setReorderingOptions;
     ubidi_writeReordered;
     ubidi_writeReverse;
+    ubrk_clone;
     ubrk_close;
     ubrk_countAvailable;
     ubrk_current;