GCC complains that inlining virStringTrimOptionalNewline is not
likely on some platforms:

  cc1: warnings being treated as errors
  ../../src/util/virfile.c: In function 'virFileReadValueBitmap':
  ../../src/util/virstring.h:292: error: inlining failed in call to 'virStringTrimOptionalNewline': call is unlikely and code size would grow [-Winline]
  ../../src/util/virfile.c:3987: error: called from here [-Winline]

Inlining this function is not going to be a measurable performance
benefit either, since the time required to execute it is going to
be dominated by running of strlen() over the string, not by the
function call overhead.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>