ucrtbase: Support overriding return value in _matherr.

dlls/ucrtbase/tests/misc.c

@@ -575,6 +575,9 @@ static struct _exception exception;
 static int CDECL matherr_callback(struct _exception *e)
 {
     exception = *e;
+
+    if (!strcmp(e->name, "acos") && e->arg1 == 2)
+        e->retval = -1;
     return 0;
 }
 
@@ -748,6 +751,7 @@ static void test_math_errors(void)
     double (CDECL *p_func3d)(double, double, double);
     double (CDECL *p_funcdl)(double, long);
     HMODULE module;
+    double d;
     int i;
 
     __setusermatherr(matherr_callback);
@@ -817,6 +821,9 @@ static void test_math_errors(void)
         ok(exception.arg2 == testsdl[i].b,
            "%s(%f, %ld) got exception arg2 %f\n", testsdl[i].func, testsdl[i].a, testsdl[i].b, exception.arg2);
     }
+
+    d = acos(2.0);
+    ok(d == -1.0, "failed to change log10 return value: %e\n", d);
 }
 
 static void test_asctime(void)