Enhance localtime_s documentation on compatibility

docs/c-runtime-library/reference/gmtime-s-gmtime32-s-gmtime64-s.md

@@ -72,6 +72,9 @@ Each of the structure fields is of type **`int`**, as shown in the following tab
 
 **`_gmtime64_s`**, which uses the **`__time64_t`** structure, allows dates to be expressed up through 23:59:59, December 31, 3000, UTC; whereas **`gmtime32_s`** only represent dates through 23:59:59 January 18, 2038, UTC. Midnight, January 1, 1970, is the lower bound of the date range for both these functions.
 
+The Microsoft-specific **`gmtime_s`** has a different signature than the C standard version. To enable the standard-conforming variant, define **`_CRT_USE_CONFORMING_ANNEX_K_TIME`** to a nonzero value before including **`<time.h>`**.
+
+
 **`gmtime_s`** is an inline function that evaluates to **`_gmtime64_s`** and **`time_t`** is equivalent to **`__time64_t`**. If you need to force the compiler to interpret **`time_t`** as the old 32-bit **`time_t`**, you can define `_USE_32BIT_TIME_T`. `_USE_32BIT_TIME_T` causes **`gmtime_s`** to be inlined as **`_gmtime32_s`**. We don't recommend `_USE_32BIT_TIME_T`, because your application may fail after January 18, 2038, and because it isn't allowed on 64-bit platforms.
 
 By default, this function's global state is scoped to the application. To change this behavior, see [Global state in the CRT](../global-state.md).

docs/c-runtime-library/reference/localtime-s-localtime32-s-localtime64-s.md

@@ -62,6 +62,8 @@ The **`localtime_s`** function converts a time stored as a [`time_t`](../standar
 > [!NOTE]
 > The target environment should try to determine whether daylight saving time is in effect.
 
+The Microsoft-specific **`localtime_s`** has a different signature than the C standard version. To enable the standard-conforming variant, define **`_CRT_USE_CONFORMING_ANNEX_K_TIME`** to a nonzero value before including **`<time.h>`**.
+
 **`_localtime64_s`**, which uses the **`__time64_t`** structure, allows dates to be expressed up through 23:59:59, January 18, 3001, coordinated universal time (UTC), whereas **`_localtime32_s`** represents dates through 23:59:59 January 18, 2038, UTC.
 
 **`localtime_s`** is an inline function that evaluates to **`_localtime64_s`**, and **`time_t`** is equivalent to **`__time64_t`**. If you need to force the compiler to interpret **`time_t`** as the old 32-bit **`time_t`**, you can define `_USE_32BIT_TIME_T`, which causes **`localtime_s`** to evaluate to **`_localtime32_s`**. We don't recommend `_USE_32BIT_TIME_T`, because your application may fail after January 18, 2038, and it isn't allowed on 64-bit platforms.