[patch, doc] Move -pthread documentation to linker options

[Sandra Loosemore]

On 12/11/2016 01:28 PM, Rainer Orth wrote:
> Hi Sandra,
>
>> PR 16519 notes that -pthread has only ever been documented as an RS6000 and
>> Solaris 2 option.  In fact it's supported by most/all(?) POSIX-flavored
>> targets, including GNU/Linux, BSD variants, Darwin, etc. It's probably best
>> to document it as a generic option, with the expectation that GCC supports
>> -pthread if the underlying operating system or C library provides an
>> implementation of the POSIX threads API.
>>
>> After scratching my head about it, it seemed that it's best categorized as
>> a linker option even though it also affects the preprocessor on some
>> targets.  I'll wait a day or two before committing the attached patch, in
>> case anybody wants to argue that this is the wrong way to categorize it.
>
> I don't like categorizing it as a linker option: as you say, it affects
> the preprocessor as well (adding -D_REENTRANT on most systems), and in
> the past (not completely sure about the present) there were subtle bugs
> if you forgot to add -pthread during compilation.

Do you have a suggestion for a better place to put it?  Preferably *one* 
place, instead of duplicating the docs in 10+ places with 
target-specific options?

-Sandra