[Ada] Work around missing Long_Long_Long_Size entry in .atp file

[Pierre-Marie de Rodat]

This prevents the compiler from giving an error message when the new
Long_Long_Long_Size entry is missing in a target configuration file.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* set_targ.adb (DTN): Fix oversight.
	(Read_Target_Dependent_Values): Do not error out on missing
	Long_Long_Long_Size entry and reuse Long_Long_Size for it.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: patch.diff
Type: text/x-diff
Size: 1301 bytes
Desc: not available
URL: <https://gcc.gnu.org/pipermail/gcc-patches/attachments/20201021/b5e5b257/attachment.bin>