Add support for hard float on M33 via CMake variable PICO_HARD_FLOAT_ABI=1

[kilograham]

Note there is currently no hard float library in the llvm_libc

[dpgeorge]

Really looking forward to this! Unless there are serious performance regressions (I expect there will not be) we will enable it in MicroPython. That's because our ABI for dynamically loadable native code only supports -mfloat-abi=soft or -mfloat-abi=hard, we don't support softfp (we could, but it's extra work and an extra combination of targets to support across all the tools).

[Wren6991]

Fairly certain the mismatched push/pop is a bug. Otherwise looks ok, so LGTM once that is re-checked

[lurch]

CI appears to be failing with:

CMake Error at src/CMakeLists.txt:72 (target_link_options):
  Cannot specify link options for target "pico_double_pico_dcp" which is not
  built by this project.
Call Stack (most recent call first):
  src/rp2_common/pico_double/CMakeLists.txt:60 (pico_wrap_function)
  src/rp2_common/pico_double/CMakeLists.txt:124 (wrap_double_functions)

[Wren6991]

CMake change in fc579bc looks weird, and may be related to CI failure. Otherwise looks like everything I mentioned was addressed so LGTM

[lurch]

Lots of CI failures in the Bazel builds now, e.g.

[1,024 / 1,094] Compiling test/hardware_sync_spin_lock_test/hardware_sync_spin_lock_test.c; 0s processwrapper-sandbox, disk-cache ... (3 actions, 2 running)
INFO: From Compiling test/pico_float_test/pico_float_test.c:
In file included from external/+_repo_rules+arm_gcc_linux-x86_64/bin/../lib/gcc/arm-none-eabi/13.2.1/../../../../arm-none-eabi/include/stdio.h:35,
                 from test/pico_float_test/pico_float_test.c:15:
test/pico_float_test/pico_float_test.c: In function 'main':
test/pico_float_test/pico_float_test.c:348:85: warning: implicit declaration of function '__real_fmaf'; did you mean '__real_fmodf'? [-Wimplicit-function-declaration]
  348 | #define check_close3(func,p0,p1,p2) ({ typeof(p0) r = func(p0,p1,p2), r2 = __CONCAT(__real_, func)(p0,p1,p2); if (isnanf(p0) || isnanf(p1) || isnanf(p2)) assert_nan(r); else assert_close(r, r2); r; })
      |                                                                                     ^~~~~~~
test/pico_float_test/pico_float_test.c:506:17: note: in expansion of macro 'check_close3'
  506 |                 check_close3(fmaf, a, b, c);
      |                 ^~~~~~~~~~~~