ld: Don't define section symbols for excluded sections

When the SEC_EXCLUDE bit is set on a section, for example, sections with
the SHF_EXCLUDE flag bit set in ELF input, the contents of the section
are excluded by the linker for non-relocatable output.  Define  __start,
__stop, .startof. and .sizeof. symbols for relocatable link or if the
SEC_EXCLUDE bit on the section is cleared.

	PR ld/34448
	* ldlang.c (lang_init_start_stop): Call lang_define_start_stop
	for relocatable link or if the SEC_EXCLUDE bit on the section
	is cleared.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>