Add missing includes in dwarf-index-write.c and mi/mi-interp.c

Add missing includes in dwarf-index-write.c and mi/mi-interp.c

The following errors show that these files are missing the include of
their matching header, add them.

  CXX    dwarf-index-write.o
/home/smarchi/src/binutils-gdb/gdb/dwarf-index-write.c: In function ‘void write_psymtabs_to_index(dwarf2_per_objfile*, const char*, const char*, const char*, dw_index_kind)’:
/home/smarchi/src/binutils-gdb/gdb/dwarf-index-write.c:1670:1: error: no previous declaration for ‘void write_psymtabs_to_index(dwarf2_per_objfile*, const char*, const char*, const char*, dw_index_kind)’ [-Werror=missing-declarations]
 write_psymtabs_to_index (struct dwarf2_per_objfile *dwarf2_per_objfile,
 ^~~~~~~~~~~~~~~~~~~~~~~

  CXX    mi/mi-interp.o
/home/smarchi/src/binutils-gdb/gdb/mi/mi-interp.c: In function ‘void mi_output_solib_attribs(ui_out*, so_list*)’:
/home/smarchi/src/binutils-gdb/gdb/mi/mi-interp.c:1030:1: error: no previous declaration for ‘void mi_output_solib_attribs(ui_out*, so_list*)’ [-Werror=missing-declarations]
 mi_output_solib_attribs (ui_out *uiout, struct so_list *solib)
 ^~~~~~~~~~~~~~~~~~~~~~~

gdb/ChangeLog:

	* dwarf-index-write.c: Include dwarf-index-write.h.
	* mi/mi-interp.c: Include mi/mi-interp.h.

Change-Id: I0103b8669e16e0fcaa476f8c5e96f49608157745