build: disable -Wenum-constexpr-conversion with clang 18

Refs: #5300
Change-Id: Ia47d73479aaaa8799efa3d5b08cf1b50b61237b6
diff --git a/.waf-tools/default-compiler-flags.py b/.waf-tools/default-compiler-flags.py
index f31b29d..16cbe28 100644
--- a/.waf-tools/default-compiler-flags.py
+++ b/.waf-tools/default-compiler-flags.py
@@ -222,6 +222,9 @@
         elif Utils.unversioned_sys_platform() == 'freebsd':
             # Bug #4790
             flags['CXXFLAGS'] += [['-isystem', '/usr/local/include']]
+        if self.getCompilerVersion(conf) >= (18, 0, 0):
+            # Bug #5300
+            flags['CXXFLAGS'] += ['-Wno-enum-constexpr-conversion']
         return flags
 
     __cxxFlags = [