[balsa] Use more compiler warnings

[Peter Bloomfield <peterb src gnome org>]

commit 64f101af82b457d78330227b533d224b96089f97
Author: Peter Bloomfield <PeterBloomfield bellsouth net>
Date:   Tue Jun 11 10:03:09 2019 -0400

    Use more compiler warnings
    
    Add -Wredundant-decls -Wshadow -Wformat-security compiler warnings
    
    * configure.ac:
    * meson.build:

 ChangeLog    | 7 +++++++
 configure.ac | 3 ++-
 meson.build  | 3 +++
 3 files changed, 12 insertions(+), 1 deletion(-)
---
diff --git a/ChangeLog b/ChangeLog
index 0b98e8d7a..9e77f87e6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2019-06-11  Peter Bloomfield  <pbloomfield bellsouth net>
+
+       Add -Wredundant-decls -Wshadow -Wformat-security compiler warnings
+
+       * configure.ac:
+       * meson.build:
+
 2019-06-10  Albrecht Dreß  <albrecht dress arcor de>
 
        Fix format string error
diff --git a/configure.ac b/configure.ac
index 6c0b72cee..fe34502bd 100644
--- a/configure.ac
+++ b/configure.ac
@@ -580,7 +580,8 @@ AC_CHECK_FUNCS([ctime_r])
 if test "$GCC" = "yes" -a "$set_more_warnings" != "no"; then
        for option in -Wsign-compare -Wpointer-arith -Wnested-externs \
             -Wchar-subscripts -Wuninitialized -Wmissing-prototypes    \
-            -Wreturn-type -Wdeclaration-after-statement ; do
+            -Wreturn-type -Wdeclaration-after-statement \
+            -Wredundant-decls -Wshadow -Wformat-security ; do
                 SAVE_CFLAGS="$CFLAGS"
                 CFLAGS="$CFLAGS $option"
                 AC_MSG_CHECKING([whether gcc understands $option])
diff --git a/meson.build b/meson.build
index 509245301..774575361 100644
--- a/meson.build
+++ b/meson.build
@@ -499,6 +499,9 @@ if balsa_from_git
   args = compiler.get_supported_arguments([
     '-Werror',
     '-Wdeprecated-declarations',
+    '-Wredundant-decls',
+    '-Wshadow',
+    '-Wformat-security',
     '-DGMIME_DISABLE_DEPRECATED',
     '-O2',
     '-U_FORTIFY_SOURCE',