[gimp] meson: fix comment about building with specific CPU instructions.

[Jehan <jehanp src gnome org>]

commit df7e319bc6ad75edf84efdd4c41900563d51f3f4
Author: Jehan <jehan girinstud io>
Date:   Wed Jun 16 00:12:02 2021 +0200

    meson: fix comment about building with specific CPU instructions.
    
    Per discussion on !262 and in particular Ell comments, the contributed
    patch was right but the comment was not. It is not just about
    g-ir-scanner and failing build. The build can still be successful yet
    the built GIMP would crash when run on a CPU not supporting all the
    extensions.

 meson.build | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
---
diff --git a/meson.build b/meson.build
index d42c0dd95c..e3191fdf4e 100644
--- a/meson.build
+++ b/meson.build
@@ -179,8 +179,12 @@ endif
 
 ################################################################################
 # Compiler CPU extensions for optimizations
-# -- Don't enable these project-wide, since some tools like g-ir-scanner,
-#    will crash on them.
+#
+# -- Don't enable these flags project-wide, only files needing them
+# should be built with a given extension, which we do with meson simd
+# module. Otherwise GIMP would end up crashing when run on CPUs which
+# don't support all the flags supported by the compiler.
+# See merge request !262 for more details.
 
 # Note that Meson has a SIMD module which can also do this for us, but it uses
 # its own #defines and we want to stay compatible with the autotools build