Link to static gpra library only on Windows. (#127)

Author: taste1981

modules/congestion_controller/BUILD.gn

@@ -31,8 +31,10 @@ rtc_library("congestion_controller") {
   if (owt_use_gpra) {
     # use Intel Goodput Rate Adapatation BWE
       include_dirs = [ owt_gpra_header_root ]
-      libs = [ "gpra_lib.lib" ]
-      lib_dirs = [ owt_gpra_lib_root ]
+      if (is_win && owt_gpra_lib_root != "") {
+        libs = [ "gpra_lib.lib" ]
+        lib_dirs = [ owt_gpra_lib_root ]
+      }
       defines += [ "INTEL_GPRA" ]
   }
 

modules/congestion_controller/goog_cc/BUILD.gn

@@ -28,8 +28,10 @@ rtc_library("goog_cc") {
   if (owt_use_gpra) {
     # use Intel Goodput Rate Adapatation BWE
       include_dirs = [ owt_gpra_header_root ]
-      libs = [ "gpra_lib.lib" ]
-      lib_dirs = [ owt_gpra_lib_root ]
+      if (is_win && owt_gpra_lib_root != "") {
+        libs = [ "gpra_lib.lib" ]
+        lib_dirs = [ owt_gpra_lib_root ]
+      }
       defines += [ "INTEL_GPRA" ]
   }