Add USE_PCIE40 flag

Pcie40Libraries/pcie40_b2slc.h

@@ -17,7 +17,9 @@
 #define SLC_RFIFO_ADD 0x00060000
 
 // Functions to read/write registers and stream files to Front End
-extern "C" { 
+#ifndef USE_PCIE40
+extern "C" {
+#endif 
 int pcie40_readfee8(int dev, int ch, int adr);
 
 int pcie40_writefee8(int dev, int ch, int adr, int val);
@@ -29,6 +31,10 @@ int pcie40_writefee32(int dev, int ch, int adr, int val);
 int pcie40_writestream(int dev, int ch, char *filename);
 
 int pcie40_writebytestream(int dev, int ch, int len, const char *bytes);
+
+#ifndef USE_PCIE40
 }
+#endif
+
 #endif // PCIE40_B2SLC_H