softmath: Use constant for log(2)

mingw-w64-crt/math/softmath/log2f.c

diff --git a/mingw-w64-crt/math/softmath/log2f.c b/mingw-w64-crt/math/softmath/log2f.c
index 443c43c..73d9659 100644
--- a/mingw-w64-crt/math/softmath/log2f.c
+++ b/mingw-w64-crt/math/softmath/log2f.c
@@ -46,5 +46,5 @@
 
 float log2f(float x)
 {
-    return softmath_logf(x) / softmath_logf(2);
+    return softmath_logf(x) / 0.69314718246459960938f;
 }