Escape double-quotes in generated #line directives

Escape double-quotes in generated #line directives

 #line directives can be generated from commands. Those may be using
double quotes. That may not be considered friendly by preprocessors when
the result looks anything like this

 #line 123 "perl -e "foo""

Input on whether the following is portable would be appreciated.

 #line 123 "perl -e \"foo\""

gcc is happy with it. I know. The world's not just win32, osx, and linux
with a choice between three compilers.