This commit simplifies native functions' prologue code by not emitting a jump opcode that goes over the function's constants pool if the pool is empty. The original code assumed the constants pool is never empty as large 32-bits constants are commonly used, but for inline assembler functions that may not be the case. This meant that inline assembler functions may start with an unneeded jump (along with its alignment byte), using four bytes more than necessary. This commit is limited to the "xtensa" target, as "xtensawin" doesn't support inline assembler functions yet, so native functions' constant pools are almost always guaranteed to hold one or more values. Signed-off-by: Alessandro Gatti <a.gatti@frob.it>