cmake: gcc: Remove no_libgcc exclusion for libgcc detection

This commit removes the `NOT no_libgcc` condition for the automatic
libgcc path detection.

The `no_libgcc` variable was previously set in this file to exclude
libgcc detection for the x86-64 targets because the x86-64 arch used
x32 ABI (`-mx32`) and the multilib for this ABI was not commonly
available. This is no longer the case (x86-64 targets now use `-m64`)
and libgcc must always be available.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>