json.h: suppress -Wzero-as-null-pointer-constant Clang warning (#5701)

Author: firewave

lib/json.h

@@ -25,10 +25,12 @@ SUPPRESS_WARNING_PUSH("-Wfloat-equal")
 SUPPRESS_WARNING_CLANG_PUSH("-Wtautological-type-limit-compare")
 SUPPRESS_WARNING_GCC_PUSH("-Wparentheses")
 SUPPRESS_WARNING_CLANG_PUSH("-Wextra-semi-stmt")
+SUPPRESS_WARNING_CLANG_PUSH("-Wzero-as-null-pointer-constant")
 
 #define PICOJSON_USE_INT64
 #include <picojson.h>
 
+SUPPRESS_WARNING_CLANG_POP
 SUPPRESS_WARNING_CLANG_POP
 SUPPRESS_WARNING_GCC_POP
 SUPPRESS_WARNING_CLANG_POP