[vte] build: Don't pass C warning flags to the C++ compiler

[Egmont Koblinger <egmontkob src gnome org>]

commit 1acae31e2db94bcd98ebbaeeca6c3dfcda025e63
Author: Christian Persch <chpe src gnome org>
Date:   Mon Sep 9 21:24:10 2019 +0200

    build: Don't pass C warning flags to the C++ compiler
    
    https://gitlab.gnome.org/GNOME/vte/issues/166
    (cherry picked from commit 740b173e06bcd38baeb6fa87232492f9bee76834)

 meson.build | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/meson.build b/meson.build
index 82266cf7..0a241be8 100644
--- a/meson.build
+++ b/meson.build
@@ -235,10 +235,8 @@ compiler_flags_common = [
   '-Wclobbered',
   '-Wempty-body',
   '-Wendif-labels',
-  '-Werror=implicit-function-declaration',
   '-Werror=init-self',
   '-Werror=missing-include-dirs',
-  '-Werror=missing-prototypes',
   '-Werror=pointer-arith',
   '-Wfloat-equal',
   '-Wignored-qualifiers',
@@ -295,6 +293,8 @@ compiler_flags_common_undesirable = [
 
 compiler_flags_c_only = [
   '-Waggregate-return',
+  '-Werror=implicit-function-declaration',
+  '-Werror=missing-prototypes',
   '-Wimplicit',
   '-Wimplicit-fallthrough=3',
   '-Wmissing-parameter-type',