This patch replaces the current function definitions with NESTED, LEAF
and END macro. They specify some more additional information about the
function; an alignment of symbol, type of symbol, stack frame usage, etc.
These information explicitly tells the assembler and the debugger about
the types of code we want to generate.

Signed-off-by: Shinya Kuribayashi <skuribay@ruby.dti.ne.jp>