Revert "Alwayze zero BSS in bbl.py"

New platforms should use ELF loaders that actually adhere to the
standard, not keep requiring this bodge. If they really find it so hard
to do that then they can have their own special builds, but this hack
should stay out of the normal QEMU build.

This reverts commit a00ccaf.

pycheribuild/projects/cross/bbl.py

@@ -62,7 +62,7 @@ class BuildBBLBase(CrossCompileAutotoolsProject):
     kernel_class = None
     cross_install_dir = DefaultInstallDir.ROOTFS_OPTBASE
     without_payload = False
-    enable_zero_bss = True
+    enable_zero_bss = False
     custom_payload: Optional[str] = None
     mem_start = "0x80000000"
     supported_architectures = (
@@ -206,6 +206,7 @@ class BuildBBLNoPayloadGFE(BuildBBLNoPayload):
     target = "bbl-gfe"
     default_directory_basename = "bbl"  # reuse same source dir
     build_dir_suffix = "-gfe"  # but not the build dir
+    enable_zero_bss = True
 
     _default_install_dir_fn = ComputedDefaultValue(
         function=_bbl_install_dir,