Applied the FreeBSD patch from Ralith, closes ticket #95 , slightly changed but basically the same. Thanx Ralith :)

dmd/constfold.c

@@ -487,6 +487,9 @@ Expression *Mod(Type *type, Expression *e1, Expression *e2)
 	    c = fmodl(e1->toReal(), r2) + fmodl(e1->toImaginary(), r2) * I;
 #elif defined(IN_GCC)
 	    c = complex_t(e1->toReal() % r2, e1->toImaginary() % r2);
+#elif defined(__FreeBSD__) && __FreeBSD_version < 800000
+        // freebsd is kinda messed up. the STABLE branch doesn't support C99's fmodl !?!
+        c = complex_t(fmod(e1->toReal(), r2), fmod(e1->toImaginary(), r2));
 #else
 	    c = complex_t(fmodl(e1->toReal(), r2), fmodl(e1->toImaginary(), r2));
 #endif
@@ -498,6 +501,9 @@ Expression *Mod(Type *type, Expression *e1, Expression *e2)
 	    c = fmodl(e1->toReal(), i2) + fmodl(e1->toImaginary(), i2) * I;
 #elif defined(IN_GCC)
 	    c = complex_t(e1->toReal() % i2, e1->toImaginary() % i2);
+#elif defined(__FreeBSD__) && __FreeBSD_version < 800000
+        // freebsd is kinda messed up. the STABLE branch doesn't support C99's fmodl !?!
+        c = complex_t(fmod(e1->toReal(), i2), fmod(e1->toImaginary(), i2));
 #else
 	    c = complex_t(fmodl(e1->toReal(), i2), fmodl(e1->toImaginary(), i2));
 #endif

dmd/mars.c

@@ -330,8 +330,10 @@ int main(int argc, char *argv[])
     global.params.os = OSLinux;
 #elif __APPLE__
     global.params.os = OSMacOSX;
+#elif __FreeBSD__
+    global.params.os = OSFreeBSD;
 #else
-#error
+#error Unsupported OS
 #endif /* linux */
 
     assert(global.params.os != OSinvalid);
@@ -843,6 +845,11 @@ int main(int argc, char *argv[])
 	global.params.tt_os = "-pc-darwin-gnu";
     break;
 
+    case OSFreeBSD:
+    VersionCondition::addPredefinedGlobalIdent("freebsd");
+    VersionCondition::addPredefinedGlobalIdent("Posix");
+    break;
+
     default:
 	assert(false && "Target OS not supported");
     }

dmd/mars.h

@@ -52,7 +52,8 @@ enum OS
     OSinvalid,
     OSLinux,
     OSWindows,
-    OSMacOSX
+    OSMacOSX,
+    OSFreeBSD
 };
 
 // Put command line switches in here