plugins: do not limit exported symbols if modules are active

plugins: do not limit exported symbols if modules are active

On Mac --enable-modules and --enable-plugins are currently incompatible, because the
Apple -Wl,-exported_symbols_list command line options prevents the export of any
symbols needed by the modules.  On x86 -Wl,--dynamic-list does not have this effect,
but only because the -Wl,--export-dynamic option provided by gmodule-2.0.pc overrides
it.  On Apple there is no -Wl,--export-dynamic, because it is the default, and thus
no override.

Either way, when modules are active there is no reason to include the plugin_ldflags.
While at it, avoid the useless -Wl,--export-dynamic when --enable-plugins is
specified but --enable-modules is not; this way, the GNU and Apple configurations
are more similar.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/516
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[AJB: fix noexport to no-export]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20210811100550.54714-1-pbonzini@redhat.com>
Cc: qemu-stable@nongnu.org