This commit makes llvm-cov avoid showing 0% (0/0) coverage for things
like file function coverage, etc. in reports and HTML output. This can happen
for files like headers that have macros but no functions. This commit makes
llvm-cov report - (0/0) instead.
rdar://29246480
Differential Revision: https://reviews.llvm.org/D26615
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@287539 91177308-0d34-0410-b5e6-96231b3b80d8
