any objections to adding -D_PTHREADS in mk/pthread.builtin.mk and pthread.buildlink.mk

[Richard PALO <richard.palo%free.fr@localhost>]

Certain pthreads based applications specifically check for _PTHREADS 
being defined, such as boost on solaris in which absence of this 
CPPFLAGS issues this type of message:

> In file included from 
> /home/pbulk/build/converters/orcus/work/.buildlink/include/boost/thread/detail/platform.hpp:17:0,
>                  from 
> /home/pbulk/build/converters/orcus/work/.buildlink/include/boost/thread/mutex.hpp:12,
>                  from pstring.cpp:35:
> /home/pbulk/build/converters/orcus/work/.buildlink/include/boost/config/requires_threads.hpp:47:5:
>  error: #error "Compiler threading support is not turned on. Please set the correct 
> command line options for threading: -pthread (Linux), -pthreads (Solaris) or -mthreads 
> (Mingw32)"
> In file included from 
> /home/pbulk/build/converters/orcus/work/.buildlink/include/boost/thread/mutex.hpp:12:0,
>                  from pstring.cpp:35:
> /home/pbulk/build/converters/orcus/work/.buildlink/include/boost/thread/detail/platform.hpp:69:9:
>  error: #error "Sorry, no boost threads are available for this platform."
> In file included from pstring.cpp:35:0:
> /home/pbulk/build/converters/orcus/work/.buildlink/include/boost/thread/mutex.hpp:18:2: 
> error: #error "Boost threads unavailable on this platform"


Since this touches pkgsrc/mk hierarchy, before I commit are there any 
objections to the following trivial patches:
> diff --git a/mk/pthread.buildlink3.mk b/mk/pthread.buildlink3.mk
> index ab6ee8a..fba35a8 100644
> --- a/mk/pthread.buildlink3.mk
> +++ b/mk/pthread.buildlink3.mk
> @@ -124,7 +124,7 @@ BUILDLINK_API_DEPENDS.${_PKG_PTHREAD}+=     ${_PKG_PTHREAD_D
>  .    include "${_PKG_PTHREAD_BUILDLINK3_MK}"
>  BUILDLINK_PREFIX.pthread=              ${BUILDLINK_PREFIX.${_PKG_PTHREAD}}
>  BUILDLINK_CFLAGS.pthread=              ${BUILDLINK_CFLAGS.${_PKG_PTHREAD}}
> -BUILDLINK_CPPFLAGS.${_PKG_PTHREAD}?=   -D_REENTRANT
> +BUILDLINK_CPPFLAGS.${_PKG_PTHREAD}?=   -D_REENTRANT -D_PTHREADS
>  BUILDLINK_CPPFLAGS.pthread=            ${BUILDLINK_CPPFLAGS.${_PKG_PTHREAD}}
>  BUILDLINK_LDFLAGS.pthread=             ${BUILDLINK_LDFLAGS.${_PKG_PTHREAD}}
>  BUILDLINK_LIBS.${_PKG_PTHREAD}?=       -lpthread
> diff --git a/mk/pthread.builtin.mk b/mk/pthread.builtin.mk
> index 733edc9..f326224 100644
> --- a/mk/pthread.builtin.mk
> +++ b/mk/pthread.builtin.mk
> @@ -69,7 +69,7 @@ BUILDLINK_LDFLAGS.pthread+=   -pthread
>  BUILDLINK_CFLAGS.pthread+=     -pthread
>  CFLAGS+=                       -D_REENTRANT
>  .    else
> -BUILDLINK_CPPFLAGS.pthread+=   -D_REENTRANT
> +BUILDLINK_CPPFLAGS.pthread+=   -D_REENTRANT -D_PTHREADS
>  .    endif
>  .    if ${OPSYS} == "FreeBSD"
>  BUILDLINK_CPPFLAGS.pthread+=   -D_THREAD_SAFE