fix p/invoke on Linux (#364)

* split p/invoke method into Windows and Linux versions

* export IsProfilerAttached() when compiling with gcc

* Revert "split p/invoke method into Windows and Linux versions"

This reverts commit e0be864.

* fix shared library name in p/invoke so it works across platforms

Author: lucaspimentel

src/Datadog.Trace.ClrProfiler.Managed/NativeMethods.cs

@@ -4,7 +4,7 @@ namespace Datadog.Trace.ClrProfiler
 {
     internal static class NativeMethods
     {
-        [DllImport("Datadog.Trace.ClrProfiler.Native.dll")]
+        [DllImport("Datadog.Trace.ClrProfiler.Native")]
         public static extern bool IsProfilerAttached();
     }
 }

src/Datadog.Trace.ClrProfiler.Native/CMakeLists.txt

@@ -16,7 +16,6 @@ add_library("Datadog.Trace.ClrProfiler.Native.static" STATIC
     il_rewriter.cpp
     integration_loader.cpp
     integration.cpp
-    interop.cpp
     logging.cpp
     metadata_builder.cpp
     miniutf.cpp
@@ -40,6 +39,7 @@ target_link_libraries("Datadog.Trace.ClrProfiler.Native.static"
 
 add_library("Datadog.Trace.ClrProfiler.Native" SHARED
     dllmain.cpp
+    interop.cpp
 )
 set_target_properties("Datadog.Trace.ClrProfiler.Native" PROPERTIES PREFIX "")
 target_link_libraries("Datadog.Trace.ClrProfiler.Native" "Datadog.Trace.ClrProfiler.Native.static")