ruleguard: add profiling labels support

[quasilyte]

When ruleguard is compiled with --tags pproflabels, profiling
will record per rules group labels, like rules:groupname.

This makes it easies to find the rules that may need to be
optimized or re-written in some other way.

Build tags protection is used to avoid the overhead in
the normal mode, when labels are not needed.

(pprof) tags
 rules: Total 2.3s
        410.0ms (18.14%): dupArg
        350.0ms (15.49%): offBy1
        250.0ms (11.06%): badLock
        160.0ms ( 7.08%): argOrder
        140.0ms ( 6.19%): equalFold
        120.0ms ( 5.31%): redundantSprint
        110.0ms ( 4.87%): wrapperFunc
         90.0ms ( 3.98%): ioutilDeprecated
         80.0ms ( 3.54%): preferFprint
         70.0ms ( 3.10%): assignOp
         60.0ms ( 2.65%): badCall
         60.0ms ( 2.65%): externalErrorReassign
         60.0ms ( 2.65%): stringXbytes
         50.0ms ( 2.21%): valSwap
         40.0ms ( 1.77%): stringConcatSimplify
         40.0ms ( 1.77%): yodaStyleExpr
         20.0ms ( 0.88%): badSorting
         20.0ms ( 0.88%): flagDeref
         20.0ms ( 0.88%): httpNoBody
         20.0ms ( 0.88%): preferStringWriter
         20.0ms ( 0.88%): timeExprSimplify
         10.0ms ( 0.44%): dynamicFmtString
         10.0ms ( 0.44%): emptyStringTest
         10.0ms ( 0.44%): preferWriteByte
         10.0ms ( 0.44%): regexpMust
         10.0ms ( 0.44%): returnAfterHttpError
         10.0ms ( 0.44%): sloppyLen
         10.0ms ( 0.44%): sprintfQuotedString