Respect the `--enable-version-specific-runtime-libs' configuration
option in libada/, so that shared gnatlib libraries will be installed
in non-version-specific $(toolexeclibdir) if requested.  In a
cross-compilation environment this helps setting up a consistent
sysroot, which can then be shared between the host and the target
system.

This lets one have `libgnarl-10.so' and `libgnat-10.so' installed in say
/usr/lib and /usr/$(target_alias)/lib for a native and a cross-build
respectively, rather than in /usr/lib/gcc/$(target_alias)/10.0.0/adalib.

Update the settings of $(toolexecdir) and $(toolexeclibdir), unused till
now, to keep the current arrangement in the version-specific case and
make the new option to be enabled by default, unlike with the other
target libraries, so as to keep existing people's build infrastructure
unaffected.

Of course if someone does use `--disable-version-specific-runtime-libs'
already, then the installation location of shared gnatlib libraries will
change, but presumably this is what they do want anyway as the current
situation where the option is ignored in libada/ only is an anomaly
really rather than one that is expected or desired.

	gcc/ada/
	* gcc-interface/Makefile.in (ADA_RTL_DSO_DIR): New variable.
	(install-gnatlib): Use it in place of ADA_RTL_OBJ_DIR for shared
	library installation.

	libada/
	* Makefile.in (toolexecdir, toolexeclibdir): New variables.
	(LIBADA_FLAGS_TO_PASS): Add `toolexeclibdir'.
	* configure.ac: Add `--enable-version-specific-runtime-libs'.
	Update version-specific `toolexecdir' and `toolexeclibdir' from
	ADA_RTL_OBJ_DIR from gcc/ada/gcc-interface/Makefile.in.
	* configure: Regenerate.

From-SVN: r276424