illumos gate

While trying to do a nondebug build, I ran into compiler errors when building uts/intel/dev. These errors do not occur during a nondebug nightly build because the dev module is normally built with "-Wno-unused -Wno-empty-body", but for some reason, my build was not specifying these flags.
I investigated the compiler errors and several of them are truly horrifying, as they lead to some code not being executed when it should. The errors are due to use of the unsafe-at-any-speed sdcmn_err*() macros:

#ifdef DEBUG
#define sdcmn_err(args) if (sdev_debug & SDEV_DEBUG) printf args
#else
#define sdcmn_err(args) /* does nothing */
#endif

Typical usage is:

if (something)
sdcmn_err("fmt", arg, arg, arg);
next_statement;

On debug builds, next_statement is executed unconditionally, but on nondebug builds, next_statement is only executed if "something".
The problem has existed at least since 2006.
We should fix these macros to be safe to use in "if" statements, and stop squelching the compiler error messages. These macros do not directly cause a malfunction, so this is just code cleanup to make them less prone to misuse.

Error messages:

../../common/fs/dev/sdev_vnops.c: In function 'sdev_rmdir':
../../common/fs/dev/sdev_vnops.c:1372: error: suggest braces around empty body in an 'if' statement [-Wempty-body]

../../common/fs/dev/sdev_ptsops.c: In function 'devpts_lookup':
../../common/fs/dev/sdev_ptsops.c:297: error: unused variable 'rvp' [-Wunused-variable]

../../common/fs/dev/sdev_zvolops.c: In function 'devzvol_validate':
../../common/fs/dev/sdev_zvolops.c:266: error: unused variable 'nm' [-Wunused-variable]
../../common/fs/dev/sdev_profile.c: In function 'prof_mknode':
../../common/fs/dev/sdev_profile.c:174: error: suggest braces around empty body in an 'if' statement [-Wempty-body]

../../common/fs/dev/sdev_profile.c: In function 'prof_filldir':
../../common/fs/dev/sdev_profile.c:697: error: suggest braces around empty body in an 'if' statement [-Wempty-bod

../../common/fs/dev/sdev_ipnetops.c: In function 'devipnet_lookup':
../../common/fs/dev/sdev_ipnetops.c:111: error: unused variable 'rvp' [-Wunused-variable]

../../common/fs/dev/sdev_vtops.c: In function 'devvt_lookup':
../../common/fs/dev/sdev_vtops.c:190: error: unused variable 'rvp' [-Wunused-variable]