Repair overflow condition where WCHAR_MAX != INT_MAX
https://github.com/andreas-schwab/tre/commit/182e1060dc3bfc175490f6e0e961d9330971299c

Add MISSING option to the default build on armv6.

PR: 194183
Submitted by: mikael.urankar@gmail.com, Adreas Schwab
Approved by: maintainer timeout (3 months without PR comment)