build(cmake): silence benign macOS ranlib and ld warnings

POSIX/SITL builds on macOS produce two classes of benign warnings that
clutter output and obscure real issues:

  ranlib: warning: 'lib*.a(foo.o)' has no symbols
  ld: warning: ignoring duplicate libraries: ...

The ranlib warnings come from sources wrapped in #if defined(CONFIG_*)
guards (i2c.cpp, spi.cpp, board_common.c, pab_manifest.c,
px4_log_history.cpp) and dummy.cpp placeholders, which legitimately
compile to empty object files on POSIX. GNU ranlib ignores this;
Apple's warns. The warning is emitted by 'ar qc' (which implicitly
builds a symbol table), not by ranlib itself, so overriding only
ARCHIVE_FINISH is insufficient. Use 'ar qcS' to skip the implicit
symbol table, then let ranlib -no_warning_for_no_symbols build it
quietly via ARCHIVE_FINISH.

The duplicate-library warnings come from CMake intentionally
re-emitting static libraries on the link line to resolve circular
dependencies between px4_layer, px4_work_queue, px4_daemon and
lockstep_scheduler. GNU ld silently dedupes; Apple's ld-prime
(Xcode 15+) warns. Pass -no_warn_duplicate_libraries to the linker.

Both fixes are Darwin-only and have no effect on Linux CI or NuttX
builds.

Signed-off-by: Ramon Roche <mrpollo@gmail.com>

platforms/posix/cmake/px4_impl_os.cmake

@@ -225,6 +225,12 @@ function(px4_os_add_flags)
 		if(UNIX AND APPLE)
 			add_definitions(-D__PX4_DARWIN)
 
+			# Silence Apple ld warning about duplicate static libs. CMake intentionally
+			# re-emits them to resolve circular deps (px4_layer, px4_work_queue,
+			# px4_daemon, lockstep_scheduler). See also CMAKE_*_ARCHIVE_FINISH override
+			# at the top of the root CMakeLists.txt for the matching ranlib silence.
+			add_link_options(LINKER:-no_warn_duplicate_libraries)
+
 		elseif(CYGWIN)
 			add_definitions(
 				-D__PX4_CYGWIN