Disable modernize-avoid-c-arrays clang-tidy check

Bug: http://b/122481018

Upcoming clang update has a clang-tidy warning about using c arrays and
instead use std::array:
    warning: do not declare C-style arrays, use std::array<> instead

Disable this warning for now (even before the new clang update lands)
since clang-tidy doesn't complain about flags it doesn't know.

Test: Build with new clang.
Change-Id: I971b84301e6cd1180326bc54711d0be193f09ccb

cmds/idmap2/Android.bp

@@ -20,6 +20,7 @@ cc_defaults {
         "misc-*",
         "modernize-*",
         "readability-*",
+        "-modernize-avoid-c-arrays",
     ],
     tidy_flags: [
         "-system-headers",