Fix build with icu >=75

Index: build/moz.configure/toolchain.configure
--- build/moz.configure/toolchain.configure.orig
+++ build/moz.configure/toolchain.configure
@@ -473,7 +473,7 @@ def check_compiler(compiler, language, target):
     # Note: MSVC, while supporting C++14, still reports 199711L for __cplusplus.
     # Note: this is a strict version check because we used to always add
     # -std=gnu++14.
-    cxx14_version = 201402
+    cxx14_version = 201703
     if info.language == 'C++':
         if info.type == 'clang' and info.language_version != cxx14_version:
             flags.append('-std=gnu++14')
