[gimp] Meson add suggested warning flags from Massimo

[Jehan <jehanp src gnome org>]

commit 3c6cf7fb3f077997f49bc7db3aced3a2fd58fe17
Author: lillolollo <4179-lillolollo users noreply gitlab gnome org>
Date:   Tue Feb 18 07:06:10 2020 +0000

    Meson add suggested warning flags from Massimo

 meson.build | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)
---
diff --git a/meson.build b/meson.build
index d4522fef5b..304c79fe4f 100644
--- a/meson.build
+++ b/meson.build
@@ -257,9 +257,19 @@ warning_cflags_common = [
   '-Wtype-limits',
 ]
 warning_cflags_c = [
+  '-Wabsolute-value',
   '-Wdeclaration-after-statement',
-  '-Wold-style-definition',
+  '-Wenum-conversion',
+  '-Wliteral-conversion',
   '-Wno-strict-prototypes',
+  '-Wold-style-definition',
+  '-Wparentheses-equality',
+  '-W#pragma-messages',
+  '-Wsometimes-uninitialized',
+  '-Wtautological-unsigned-enum-zero-compare',
+  '-Wunneeded-internal-declaration',
+  '-Wunused-function',
+  '-Wunused-value',
 
   '-Werror=implicit-function-declaration',
 ]