Use -Wmacro-redefined flag to warn redefined macros by clang.

#define MY_DEFINE   111
#define MY_DEFINE   222

int main(void)
{
    return 0;
}

$ # M1 Mac (Ventura) + Apple clang 14.0.0
$ clang sample.cpp -Wmacro-redefined
sample.cpp:2:9: warning: 'MY_DEFINE' macro redefined [-Wmacro-redefined]
#define MY_DEFINE   222
        ^
sample.cpp:1:9: note: previous definition is here
#define MY_DEFINE   111
        ^
1 warning generated.

The warnings are displayed automatically: clang enables -Wmacro-redefined by default.

$ # M1 Mac (Ventura) + Apple clang 14.0.0
$ clang sample.cpp
sample.cpp:2:9: warning: 'MY_DEFINE' macro redefined [-Wmacro-redefined]
#define MY_DEFINE   222
        ^
sample.cpp:1:9: note: previous definition is here
#define MY_DEFINE   111
        ^
1 warning generated.

Suppress warnings

Use -Wno-macro-redefined to suppress warnings.

$ # M1 Mac (Ventura) + Apple clang 14.0.0
$ clang sample.cpp -Wno-macro-redefined
$

GCC

GCC also accepts -Wmacro-redefined. On macOS, gcc is an alias of clang: we need to use gcc-N (N: the version of gcc) instead.

$ # M1 Mac (Ventura) + gcc 12.2.0
$ gcc-12 sample.cpp
$sample.cpp:2: warning: "MY_DEFINE" redefined
    2 | #define MY_DEFINE   222
      | 
sample.cpp:1: note: this is the location of the previous definition
    1 | #define MY_DEFINE   111
      |

References