[master] f633c8e54 build: Don't warn on system headers

[Dridi Boukelmoune]

commit f633c8e54d8dbbc0568ececeb7bb942c06aca0c4
Author: Dridi Boukelmoune <dridi.boukelmoune at gmail.com>
Date:   Tue Jul 6 15:16:44 2021 +0200

    build: Don't warn on system headers
    
    Since we turn warnings into errors, that means failing the build because
    something we have no control over in /usr/include does not have a strict
    prototype or some other shenanigan.
    
    Just in case it might be added by Wall or Wextra in a future clang or
    GCC release, we may disable it explicitly too.
    
    Refs #3565

diff --git a/wflags.py b/wflags.py
index ce32037c4..9e9e4e902 100644
--- a/wflags.py
+++ b/wflags.py
@@ -61,7 +61,6 @@ DESIRABLE_WFLAGS = [
     "-Wstrict-prototypes",
     "-Wstring-plus-int",
     "-Wswitch",
-    "-Wsystem-headers",
     "-Wunused-parameter",
     "-Wunused-parameters",
     "-Wunused-result",
@@ -69,15 +68,12 @@ DESIRABLE_WFLAGS = [
 ]
 
 UNDESIRABLE_WFLAGS = [
+    "-Wno-system-headers" # Outside of our control
     "-Wno-thread-safety", # Does not understand our mutexs are wrapped
     "-Wno-old-style-definition", # Does not like vgz
     "-Wno-sign-compare", # Fixable
     "-Wno-implicit-fallthrough", # Probably Fixable
-    "-Wno-builtin-requires-header", # Complains about linux::pthread.h
-    "-Wno-incomplete-setjmp-declaration", # Clang complains about glibc::pthread.h
-    "-Wno-redundant-decls", # Complains about centos::stdio.h
     "-Wno-missing-variable-declarations", # Complains about optreset
-    "-Wno-parentheses", # GCC complains about musl::endian.h
     "-Wno-nullability-completeness", # Barfs all over MacOSx
 ]