The R_RISCV_LPAD relocation can be used for PLT entry generation and also for
linker relaxation. Additionally, we defined a new mapping symbol type to help
users understand the function signature for the corresponding function.

The addend value is the label value, and it will point to the mapping symbol
placed at the beginning of the function.

e.g.
```asm
foo:         # void foo(void)
$sFvvE:
    lpad 123 # R_RISCV_LPAD $sFvvE + 123
```

We propose two linker relaxations for the landing pad. The first is removing
the entire landing pad, which can be used when symbols have local visibility,
and the address is not taken by any other reference. The second is a landing
pad scheme conversion, designed for backward compatibility (or as a workaround)
for legacy programs that may use functions without declarations.

Rephase to make it clearly about it can remove instruction.

- Drop the restriction of static link
- Emphasis must be applied to all `R_RISCV_LPAD`
- GNU property and PLT entries must adjust too.

… table

- Updated the relaxation condition to apply only when the symbol is not
  exported to the dynamic symbol table.