Make llvm-profdata show -text work as advertised in the documentation.

Per LLVM's CommandGuide, llvm-profdata show -text is supposed to produce
textual output that can be passed as input to further llvm-profdata
invocations. This previously didn't work for two reasons:

1) -text was not sufficient to enable the machine-readable text format output;
instead, -text was effectively ignored if -counts was not also specified. (With
this patch, -counts is instead ignored if -text is specified, because the
machine-readable text format always includes counts.)

2) When the input data was an IR-level profile, the :ir marker was missing from
the output, resulting in a text format output that would not be usable as
profiling data due to function hash mismatches.

Differential Revision: https://reviews.llvm.org/D51188

llvm-svn: 340592