Kernel+Toolchain: Use .init_array section for global constructors

Before this change, our dynamic linker's global constructor handler
relied on the GNU linker implicitly including the content of `.ctors`
section inside `.init_array`. The mold linker does not do this, so
global constructors would fail to be called in the mold-built userland.

There is no point in sticking to `.ctors`, as most other systems already
use the superior `.init_array` scheme. This commit changes the kernel
linker script to not discard this new section, and enables it by default
in our toolchain.

Toolchain/BuildIt.sh

@@ -379,6 +379,7 @@ pushd "$DIR/Build/$ARCH"
                                             --enable-default-pie \
                                             --enable-lto \
                                             --enable-threads=posix \
+                                            --enable-initfini-array \
                                             ${TRY_USE_LOCAL_TOOLCHAIN:+"--quiet"} || exit 1
 
         echo "XXX build gcc and libgcc"