package/ply: needs dynamic library

package/ply: needs dynamic library

ply builds and installs a library. Some objects that go in that library
are tagged with a 'section' attribute (excerpt):

    __attribute__((section("providers")))

Later on, it references the bounds of that section, with the canonical
__start and __stop markers, which will eventually be created by the
linker:

    extern struct provider __start_providers;
    extern struct provider __stop_providers;

Sections only exists in an ELF file, and a static library id not an ELF.
So, when creating a static library, the markers are not created. Thus,
when linking the final executable, the link fails because of missing
symbols:

    .../powerpc-buildroot-linux-uclibc/bin/ld: ../libply/.libs/libply.a(libply_la-provider.o): in function `provider_get':
    provider.c:(.text+0xe): undefined reference to `__start_providers'
    .../powerpc-buildroot-linux-uclibc/bin/ld: provider.c:(.text+0x12): undefined reference to `__stop_providers'
    .../powerpc-buildroot-linux-uclibc/bin/ld: provider.c:(.text+0x2a): undefined reference to `__start_providers'
    .../powerpc-buildroot-linux-uclibc/bin/ld: provider.c:(.text+0x32): undefined reference to `__stop_providers'

So, conceptually, ply can not build in static-only.

Fixes:
 - http://autobuild.buildroot.net/results/3a586241d37614b644ff6c4674ae28df2b22fdf8

Signed-off-by: Andreas Klinger <ak@it-klinger.de>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>