MFC r295900, r295768 to usr.sbin/iostat

r295768 | asomers | 2016-02-18 13:08:01 -0700 (Thu, 18 Feb 2016) | 14 lines

Fix compiler warnings in iostat

Raise WARNS from 1 to 6 (the default)
Fix warnings:

• Use C99 designated initializers for structs, and initialize all fields
• Mark global variables as static
• Mark unused function arguments
• Be careful about signed/unsigned comparisons

r295900 | asomers | 2016-02-22 14:40:53 -0700 (Mon, 22 Feb 2016) | 10 lines

Fix the usr.sbin/iostat build with GCC, broken by r295768

Renamed some local variables for compatibility with -Wshadow