gdb: add 'maint set/show gnu-source-highlight enabled' command

In a later commit I want to address an issue with the Python pygments
based code styling solution.  As this approach is only used when the
GNU Source Highlight library is not available, testing bugs in this
area can be annoying, as it requires GDB to be rebuilt with use of GNU
Source Highlight disabled.

This commit adds a pair of new maintenance commands:

  maintenance set gnu-source-highlight enabled on|off
  maintenance show gnu-source-highlight enabled

these commands can be used to disable use of the GNU Source Highlight
library, allowing me, in a later commit, to easily test bugs that
would otherwise be masked by GNU Source Highlight being used.

I made this a maintenance command, rather than a general purpose
command, as it didn't seem like this was something a general user
would need to adjust.  We can always convert the maintenance command
to a general command later if needed.

There's no test for this here, but this feature will be used in a
later commit.

1 files changed, 8 insertions, 0 deletions

diff --git a/gdb/NEWS b/gdb/NEWS
index 73eb022..c1f3056 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -73,6 +73,14 @@ show debug linux-nat
 maint flush source-cache
   Flush the contents of the source code cache.
 
+maint set gnu-source-highlight enabled on|off
+maint show gnu-source-highlight enabled
+  Whether GDB should use the GNU Source Highlight library for adding
+  styling to source code.  When off, the library will not be used, even
+  when available.  When GNU Source Highlight isn't used, or can't add
+  styling to a particular source file, then the Python Pygments
+  library will be used instead.
+
 * Changed commands
 
 maint packet