add DLLEXPORT to bsdsrc files

bsdsrc/b_exp.c

@@ -82,7 +82,7 @@ static const double lntiny = -0x1.77af8ebeae354p9;
 static const double invln2 = 0x1.71547652b82fep0;
 
 #if 0
-double exp(x)
+DLLEXPORT double exp(x)
 double x;
 {
 	double  z,hi,lo,c;

bsdsrc/b_log.c

@@ -352,7 +352,7 @@ static double logF_tail[N+1] = {
 };
 
 #if 0
-double
+DLLEXPORT double
 #ifdef _ANSI_SOURCE
 log(double x)
 #else

bsdsrc/b_tgamma.c

@@ -121,7 +121,7 @@ static struct Double ratfun_gam(double, double);
 
 static const double zero = 0., one = 1.0, tiny = 1e-300;
 
-double
+DLLEXPORT double
 tgamma(x)
 	double x;
 {