G++ ignores _Pragma diagnostic ignored

I am trying to disable g++ warnings in code expanded from macros. By my understanding, _Pragma should follow macro usage and this should not trigger Wparentheses when being compiled with g++:

#include <stdio.h>

#define TEST(expr) \
    int a = 1; \
    _Pragma( "GCC diagnostic push" ) \
    _Pragma( "GCC diagnostic ignored \"-Wparentheses\"" ) \
    if (a <= expr) { \
        printf("filler\n"); \
    } \
    _Pragma( "GCC diagnostic pop" )

int main(){
    int b = 2, c = 3;
    TEST(b == c);
}

When I compile this with g++, I get Wparentheses warning, which I am trying to disable.

xarn@DESKTOP-B2A3CNC:/mnt/c/ubuntu$ g++ -Wall -Wextra test3.c
test3.c: In function ‘int main()’:
test3.c:8:11: warning: suggest parentheses around comparison in operand of ‘==’ [-Wparentheses]
     if (a <= expr) { \
           ^
test3.c:15:5: note: in expansion of macro ‘TEST’
     TEST(b == c);
     ^

However it works as expected when using gcc:

xarn@DESKTOP-B2A3CNC:/mnt/c/ubuntu$ gcc -Wall -Wextra test3.c
test3.c: In function ‘main’:
test3.c:16:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^

I am using g++ version 4.8.5.