Make sure the build script pulls the right CFLAGS and prevent -Werror.

--- a/setup.py
+++ b/setup.py
@@ -750,7 +750,7 @@
     #we have to add the python cflags:
     if not (is_Fedora() or is_Debian() or is_CentOS() or is_RedHat() or is_AlmaLinux() or is_RockyLinux() or is_OracleLinux() or is_openSUSE()):
         import sysconfig
-        for cflag in shlex.split(sysconfig.get_config_var('CFLAGS') or ''):
+        for cflag in shlex.split(sysconfig.get_config_var('BUILD_CFLAGS') or ''):
             add_to_keywords(kw, 'extra_compile_args', cflag)
 
     def add_tokens(s, add_to="extra_link_args"):
@@ -809,7 +809,7 @@
             #as of Cython 0.26 + clang 4.0. Other version combinations may require
             #(un)commenting other switches.
             if not hascflag("-Wno-error"):
-                addcflags("-Werror")
+                addcflags("-Wno-error")
             addcflags(
                 "-Wno-deprecated-register",
                 "-Wno-unused-command-line-argument",
@@ -823,7 +823,7 @@
                 )
         else:
             if not hascflag("-Wno-error"):
-                addcflags("-Werror")
+                addcflags("-Wno-error")
             if NETBSD:
                 #see: http://trac.cython.org/ticket/395
                 addcflags("-fno-strict-aliasing")