This was causing segfaults in the MH test suite when building with
glibc 2.26 on x86_64.
* gnu/packages/patches/mailutils-uninitialized-memory.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/mail.scm (mailutils)[source](patches, snippet): New
fields.
[native-inputs]: New field.
Ludovic Courtès