Expose ABTSTK via OS_ReadSysInfo 6

It's the only privileged-mode stack which doesn't have its address
exposed via OS_ReadSysInfo 6. Expose it so that software which wants to
know its address can read it instead of relying on hardcoded values.

Tested on Raspberry Pi 4

Version 6.50. Tagged as 'Kernel-6_50'

VersionASM

@@ -9,12 +9,12 @@
                         GBLS    Module_ApplicationDate
                         GBLS    Module_HelpVersion
                         GBLS    Module_ComponentName
-Module_MajorVersion     SETS    "6.49"
-Module_Version          SETA    649
+Module_MajorVersion     SETS    "6.50"
+Module_Version          SETA    650
 Module_MinorVersion     SETS    ""
-Module_Date             SETS    "23 Jan 2021"
-Module_ApplicationDate  SETS    "23-Jan-21"
+Module_Date             SETS    "30 Jan 2021"
+Module_ApplicationDate  SETS    "30-Jan-21"
 Module_ComponentName    SETS    "Kernel"
-Module_FullVersion      SETS    "6.49"
-Module_HelpVersion      SETS    "6.49 (23 Jan 2021)"
+Module_FullVersion      SETS    "6.50"
+Module_HelpVersion      SETS    "6.50 (30 Jan 2021)"
                         END

VersionNum

-/* (6.49)
+/* (6.50)
  *
  * This file is automatically maintained by srccommit, do not edit manually.
  *
  */
-#define Module_MajorVersion_CMHG        6.49
+#define Module_MajorVersion_CMHG        6.50
 #define Module_MinorVersion_CMHG
-#define Module_Date_CMHG                23 Jan 2021
+#define Module_Date_CMHG                30 Jan 2021
 
-#define Module_MajorVersion             "6.49"
-#define Module_Version                  649
+#define Module_MajorVersion             "6.50"
+#define Module_Version                  650
 #define Module_MinorVersion             ""
-#define Module_Date                     "23 Jan 2021"
+#define Module_Date                     "30 Jan 2021"
 
-#define Module_ApplicationDate          "23-Jan-21"
+#define Module_ApplicationDate          "30-Jan-21"
 
 #define Module_ComponentName            "Kernel"
 
-#define Module_FullVersion              "6.49"
-#define Module_HelpVersion              "6.49 (23 Jan 2021)"
-#define Module_LibraryVersionInfo       "6:49"
+#define Module_FullVersion              "6.50"
+#define Module_HelpVersion              "6.50 (30 Jan 2021)"
+#define Module_LibraryVersionInfo       "6:50"

hdr/OSRSI6

@@ -87,5 +87,6 @@ OSRSI6_ECFShift                                * 84
 OSRSI6_VecPtrTab                               * 85
 OSRSI6_NVECTORS                                * 86
 OSRSI6_CAMFormat                               * 87 ; 0 = 8 bytes per entry, 1 = 16 bytes per entry
+OSRSI6_ABTSTK                                  * 88
 
         END

s/Middle

@@ -1584,6 +1584,7 @@ osri6_table
     DCD  ZeroPage+VecPtrTab                           ;85
     DCD  NVECTORS                                     ;86
     DCD  1                                            ;87 CAM format: 0 = 8 bytes/entry, 1 = 16 bytes/entry
+    DCD  ABTSTK                                       ;88
 osri6_maxvalue * (.-4-osri6_table) :SHR: 2