[UCRTBASE] Implement simplistic versions of some stubs

This is to allow ucrtbase_winetest to run without debug breaks.
Proper implementations will follow.

Author: tkreuzer

dll/win32/ucrtbase/stubs.c

@@ -1,6 +1,9 @@
 
 #include <stdint.h>
 #include <intrin.h>
+#include <malloc.h>
+#define _USE_MATH_DEFINES
+#include <math.h>
 
 // atexit is needed by libsupc++
 extern int __cdecl _crt_atexit(void (__cdecl*)(void));
@@ -9,13 +12,11 @@ int __cdecl atexit(void (__cdecl* function)(void))
     return _crt_atexit(function);
 }
 
-void* __cdecl malloc(size_t);
 void* __cdecl operator_new(size_t size)
 {
     return malloc(size);
 }
 
-void free(void*);
 void _cdecl operator_delete(void *mem)
 {
     free(mem);
@@ -48,26 +49,25 @@ int __cdecl __acrt_initialize_sse2(void)
 
 double fma(double x, double y, double z)
 {
-    __debugbreak();
-    return 0.;
+    // Simplistic implementation
+    return (x * y) + z;
 }
 
 float fmaf(float x, float y, float z)
 {
-    __debugbreak();
-    return 0.;
+    // Simplistic implementation
+    return (x * y) + z;
 }
 
 double log2(double x)
 {
-    __debugbreak();
-    return 0.;
+    // Simplistic implementation: log2(x) = log(x) / log(2)
+    return log(x) * M_LOG2E;
 }
 
 float log2f(float x)
 {
-    __debugbreak();
-    return 0.;
+    return (float)log2((double)x);
 }
 
 long int lrint(double x)