x11/gmrun: Fix build with GCC architectures [1]

• Add USES=compiler:c++11-lang [1]
• Include cstring in src/ci_string.h [1]
• Add USES=gnome localbase:ldflags [1]
• While here, add mising dependencies and pet portlint

PR: 237871 [1]
Submitted by: pkubaj@
Sponsored by: Rubicon Communications, LLC (Netgate)