Rename _bsr/_bsf to bsr/bsf

Now that these functions are behind _COSMO_SOURCE there's no reason for
having the ugly underscore anymore. To use these functions, you need to
pass -mcosmo to cosmocc.

tool/emacs/cosmo-c-builtins.el

@@ -190,6 +190,9 @@
            "__integer_pack"
            "__is_same"))
 
+        (cuda-builtin-types
+         '("__syncthreads"))
+
         (cosmopolitan-builtin-defines
          '("COSMOPOLITAN_CXX_START_"
            "COSMOPOLITAN_CXX_END_"
@@ -225,6 +228,7 @@
                                 gcc-builtin-functions-sync
                                 gcc-builtin-functions-ia32
                                 gxx-builtin-type-traits
+                                cuda-builtin-types
                                 cosmopolitan-builtin-defines
                                 cosmopolitan-builtin-functions))
             "\\_>")))