[Ada] Deconstruct 'F' as a prefix for an ALI data

In GNATprove we used to store a variant of cross-reference information in
the ALI file in lines that started with an 'F' letter. This is no longer
the case, so the letter can be returned to the pool of unused prefixes.

2018-07-31  Piotr Trojanek  <trojanek@adacore.com>

gcc/ada/

	* ali.adb (Known_ALI_Lines): Remove 'F' as a prefix for lines
	related to the FORMAL analysis done by GNATprove.

From-SVN: r263092

gcc/ada/ChangeLog

+2018-07-31  Piotr Trojanek  <trojanek@adacore.com>
+
+	* ali.adb (Known_ALI_Lines): Remove 'F' as a prefix for lines
+	related to the FORMAL analysis done by GNATprove.
+
 2018-07-31  Javier Miranda  <miranda@adacore.com>
 
 	* sem.ads (Inside_Preanalysis_Without_Freezing): New global

gcc/ada/ali.adb

@@ -39,7 +39,7 @@ package body ALI is
    --  line type markers in the ALI file. This is used in Scan_ALI to detect
    --  (or skip) invalid lines. The following letters are still available:
    --
-   --    B G H J K O Q Z
+   --    B F G H J K O Q Z
 
    Known_ALI_Lines : constant array (Character range 'A' .. 'Z') of Boolean :=
      ('V'    => True,   -- version
@@ -59,7 +59,6 @@ package body ALI is
       'Y'    => True,   -- limited_with
       'Z'    => True,   -- implicit with from instantiation
       'C'    => True,   -- SCO information
-      'F'    => True,   -- SPARK cross-reference information
       'T'    => True,   -- task stack information
       others => False);