[Ada] Accept square brackets for expression functions

[Pierre-Marie de Rodat]

Ada RM 6.8 allows an expression function to return an aggregate directly
at the top level (enclosed with either parentheses or square brackets).

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

gcc/ada/

	* par-ch6.adb (Scan_Body_Or_Expression_Function): Accept left
	bracket as token to open an expression function.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: patch.diff
Type: text/x-diff
Size: 725 bytes
Desc: not available
URL: <https://gcc.gnu.org/pipermail/gcc-patches/attachments/20220111/51a498c5/attachment.bin>