Use std::log overload from <cmath> instead of std::logl

Many of the [fl] suffix math functions are missing from namespace std
due to a bug in the C++ standard library under gcc.

libid/bigflt.cpp

@@ -680,7 +680,7 @@ bf_t unsafe_ln_bf(bf_t r, bf_t n)
     }
 
     f = bf_to_float(n);
-    f = logl(f); // approximate ln(x)
+    f = std::log(f); // approximate ln(x)
     // no need to check overflow
     // appears to be ok, do ln
 

libid/bignum.cpp

@@ -916,7 +916,7 @@ bn_t unsafe_ln_bn(bn_t r, bn_t n)
     }
 
     f = bn_to_float(n);
-    f = logl(f); // approximate ln(x)
+    f = std::log(f); // approximate ln(x)
     maxval = (1L << ((g_int_length << 3)-1)) - 1;
     if (f > maxval) // check for overflow
     {

libid/fpu087.cpp

@@ -104,7 +104,7 @@ void fpu_cmplx_log(const DComplex *x, DComplex *z)
     }
     if (x->y == 0.0)// x is real
     {
-        z->x = std::logl(x->x);
+        z->x = std::log(x->x);
         z->y = 0.0;
         return;
     }