Darwin: Revise handling of some driver opts.

Darwin: Revise handling of some driver opts.

[Fixes a regression in driver output with empty comand lines, also a pre-
 requisite for fixes in PR80556]

Darwin has a user convenience feature where some linker options are exposed
at the driver level (so one can type '-all_load' instead of '-Wl,-all_load'
or '-Xlinker -all_load').  We retain this feature, but now these options are
all marked as 'Driver' and we process them as early as possible so that they
get allocated to the right toolchain command.  There are a couple of special
cases where these driver opts are used multiple times, or to control
operations on more than one command (e.g. dynamiclib).  These are handled
specially and we then add %<xxxx specs for the commands that _do not_ need
them.  NOTE: the ordering of 'shared' and 'dynamiclib' is significant, hence
they are placed out of alphabetical order at the start.  Likewise, we keep
a couple of cases where a negative option originally appeared after the
positive alternate, potentially overriding it.

When we report an error with %e, it seems necessary to strip the option
before doing so, otherwise it survives to the cc1 command line (%e does not
appear to abort the program before this).

Right now there is no mechanism to split up the 'variable portion' (%*) of
the matched spec string, so where we have some driver specs that take 2 or
3 arguments, these cannot be processed here, but are deferred until the
LINK_SPEC, where they are copied verbatim.

We have a 'safe' version of the macOS version string, that has been sanity-
checked and truncated to minor version.  If the 'tiny' (3rd) portion of the
value is not significant, it is better to use the safe one in version-compare().

We were not wrapping all the default libraries in checks for whether
they should be used.  We were also wasting a process launch calling
dsymutil for 'r' link lines (a NOP in practice).  Order the checks
that exclude linking from most likely to occur, downwards.

We were pushing a spec value for weak_reference_mismatches unconditionally
which is not needed (the value was the default) and the side-effect of
this was that we appeared to need to drive a link command; leading to
unexpected diagnostics for cases where gcc was invoked with an empty
command line.

Also we were pushing flags for sysroot, os minimum version and controls
even if the command line was empty.

Backported from 353cb291a486af3be93dd9320dde9e38b542a1bd,
4aef14b09557ce072f1269bd8a05fa2b1df0eda2 and
ff56eea24e48f7a8a3b39db7049d1da532d4b8af

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
gcc/ChangeLog:

	* config/darwin-driver.c (darwin_driver_init): Revise comments, handle
	filelist and framework options in specs instead of code. Exit from the
	option handling early if the command line is definitely enpty.
	* config/darwin.h (SUBTARGET_DRIVER_SELF_SPECS): Update to handle link
	specs that are really driver ones. Remove setting for the default content
	of weak_reference_mismatches
	(DARWIN_CC1_SPEC): Likewise.
	(CPP_SPEC): Likewise.
	(SYSROOT_SPEC): Append space.
	(LINK_SYSROOT_SPEC): Remove most driver link specs.
	(STANDARD_STARTFILE_PREFIX_2): Update link-related specs.
	(STARTFILE_SPEC): Likewise.
	(ASM_MMACOSX_VERSION_MIN_SPEC): Fix line wrap.
	(ASM_SPEC): Update driver-related specs.
	(ASM_FINAL_SPEC): Likewise.
	(LINK_COMMAND_SPEC_A): Update 'r' handling to skip gomp and itm when r
	or nodefaultlibs is given.
	(DSYMUTIL_SPEC): Do not call dsymutil for '-r' link lines.
	Update ordering of exclusions, remove duplicate 'v' addition
	(collect2 will add this from the main command line).
	* config/darwin.opt: Remove now unused option aliases.
	* config/i386/darwin.h (EXTRA_ASM_OPTS): Ensure space after opt.
	(ASM_SPEC): Update driver-related specs.