[Bug c/19541] need another option to support what -I- did just besides -iquote

[rodolfo at rodsoft dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19541

--- Comment #23 from Rodolfo Schulz de Lima <rodolfo at rodsoft dot org> ---
How difficult is it to add a parameter to add paths to precompiled header
search list *only*? 

We have a big code base with #include "pch.h" in some source files. 
If source file directory is always searched first for headers, this breaks
out-of-source builds, unless the precompiled header is generated in the source
tree. For read-only source trees, this "solution" is unacceptable.

The ideal solution would be a parameter like -ipch <path> that adds <path> to
be searched for precompiled headers *before* the current source directory.

I could spend some time creating a patch, but seeing that others have come with
patches that weren't applied, this kind of demotivate me.