[ada, build] Avoid cp -p failures during Ada make install

[Rainer Orth]

Prompted by a known make install failure on Linux/x86_64, I decided to
finally rework my ancient patch

	http://gcc.gnu.org/ml/gcc-patches/2014-04/msg01669.html

along the lines Mike suggested back then, i.e. use cp && touch -r
instead of cp -p.  This avoids the failures like

for file in rts/*.ad[sb]*; do \
    cp -p $file /vol/gcc/obj/gcc/gcc-10/vol/gcc/lib/gcc/x86_64-pc-linux-gnu/10.0.0/adainclude; \
done
cp: preserving permissions for ‘/vol/gcc/obj/gcc/gcc-10/vol/gcc/lib/gcc/x86_64-pc-linux-gnu/10.0.0/adainclude/a-assert.adb’: Operation not supported

when installing e.g. to an NFSv3 destination which doesn't support POSIX
ACLs from a local filesystem that does.

The fix turned out to be a bit more involved than I initially thought:

* I've changed INSTALL_DATA_DATE to use GNU make's $(call) function
  since the args are now needed twice.

* The destination argument now needs to include the filename: while cp
  can use a directory as destination, touch -r needs the full filename
  to preserve the timestamps.

* In order for $(notdir) to work which operates textually on its args,
  the loops had to be changed from shell for loops to make $(foreach)
  loops.

* And finally, to avoid exceeding the command line length limit, the
  individual commands have been separate by newlines, a trick learned
  from https://stackoverflow.com/questions/7039811/how-do-i-process-extremely-long-lists-of-files-in-a-make-recipe

When first testing this, the make install failed trying to install
standard.ads.h: while this gave just a warning with the old code

cp: cannot stat 'rts/standard.ads.h': No such file or directory

it now fails.  It turns out this is a dangling symlink

$ ls -l gcc/ada/rts/standard.ads.h
lrwxrwxrwx 1 ro gcc 50 May  7 18:13 gcc/ada/rts/standard.ads.h -> /vol/gcc/src/hg/trunk/local/gcc/ada/standard.ads.h
$ ls -lL gcc/ada/rts/standard.ads.h
ls: cannot access 'gcc/ada/rts/standard.ads.h': No such file or directory

introduced in r260921.  This is only present on mainline and the gcc-9
branch and the file seems never to have existed in tree, so I'm just
removing the reference.

Tested on x86_64-pc-linux-gnu installing both to a local filesystem and
an NFSv3 filesystem.

Ok for mainline (and the gcc-9 and gcc-8 branches eventually)?

Thanks.
	Rainer

-- 
-----------------------------------------------------------------------------
Rainer Orth, Center for Biotechnology, Bielefeld University


2019-05-04  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	* Makefile.rtl (LIBGNAT_SRCS): Remove standard.ads.h.
	* gcc-interface/Makefile.in (INSTALL_DATA_DATE): Replace cp -p
	with cp && touch -r.
	(NL): Define.
	(install-gcc-specs, install-gnatlib): Adapt INSTALL_DATA_DATE
	uses.  Switch to $(foreach).  Separate commands by $(NL).

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