silence -Wunreachable-code-loop-increment

This warning is going to be enabled and become an error. It fires here:
external/icu/icu4c/source/i18n/numparse_compositions.cpp:67 . A comment
above the loop clarifies that the loop is "meant to be used for boundary
checking," and is only meant to run up to once.

Bug: 150166387
Test: TreeHugger
Change-Id: Ic8ff81da4d70ab807ff310ea701b077b738c624f
diff --git a/icu4c/source/i18n/Android.bp b/icu4c/source/i18n/Android.bp
index 48ac41b..a6f7ee6 100644
--- a/icu4c/source/i18n/Android.bp
+++ b/icu4c/source/i18n/Android.bp
@@ -31,6 +31,7 @@
         "-Wno-unused-parameter",
         "-Wno-unused-const-variable",
         "-Wno-unneeded-internal-declaration",
+        "-Wno-unreachable-code-loop-increment",
     ],
     cppflags: [
         "-std=c++11",