Modify arg passing info for struct with one int and one fp to match GCC

behavior.

Author: Jim Wilson

riscv-elf.md

@@ -209,8 +209,9 @@ either order, is passed in a floating-point register and an integer register,
 with the integer zero- or sign-extended as though it were a scalar, provided
 the floating-point real is no more than FLEN bits wide and the integer is no
 more than XLEN bits wide, and at least one floating-point argument register
-and at least one integer argument register is available.  Otherwise, it is
-passed according to the integer calling convention.
+and at least one integer argument register is available, with the integer
+placed in its argument register without extension to XLEN bits.  Otherwise,
+it is passed according to the integer calling convention.
 
 Unions are never flattened and are always passed according to the integer
 calling convention.