Make both SK_API definition points identical and order independent.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2189983002

Review-Url: https://codereview.chromium.org/2189983002
diff --git a/BUILD.gn b/BUILD.gn
index 7459fb0..d4ccf63 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -8,6 +8,7 @@
 
 skia_public_includes = [
   "include/android",
+  "include/c",
   "include/codec",
   "include/config",
   "include/core",
@@ -21,8 +22,6 @@
   "include/utils",
   "include/utils/mac",
   "include/xml",
-
-  "include/c",  # TODO: move back to top, order shouldn't matter
 ]
 
 # Skia public API, generally provided by :skia.
diff --git a/include/c/sk_types.h b/include/c/sk_types.h
index 41dd271..dcbc6f7 100644
--- a/include/c/sk_types.h
+++ b/include/c/sk_types.h
@@ -23,8 +23,20 @@
     #define SK_C_PLUS_PLUS_END_GUARD
 #endif
 
-#ifndef SK_API
-#define SK_API
+#if !defined(SK_API)
+    #if defined(SKIA_DLL)
+        #if defined(SK_BUILD_FOR_WIN32)
+            #if SKIA_IMPLEMENTATION
+                #define SK_API __declspec(dllexport)
+            #else
+                #define SK_API __declspec(dllimport)
+            #endif
+        #else
+            #define SK_API __attribute__((visibility("default")))
+        #endif
+    #else
+        #define SK_API
+    #endif
 #endif
 
 ///////////////////////////////////////////////////////////////////////////////////////
diff --git a/include/core/SkPreConfig.h b/include/core/SkPreConfig.h
index 8c8eeef..f993920 100644
--- a/include/core/SkPreConfig.h
+++ b/include/core/SkPreConfig.h
@@ -209,18 +209,20 @@
     #define SKIA_IMPLEMENTATION 0
 #endif
 
-#if defined(SKIA_DLL)
-    #if defined(SK_BUILD_FOR_WIN32)
-        #if SKIA_IMPLEMENTATION
-            #define SK_API __declspec(dllexport)
+#if !defined(SK_API)
+    #if defined(SKIA_DLL)
+        #if defined(SK_BUILD_FOR_WIN32)
+            #if SKIA_IMPLEMENTATION
+                #define SK_API __declspec(dllexport)
+            #else
+                #define SK_API __declspec(dllimport)
+            #endif
         #else
-            #define SK_API __declspec(dllimport)
+            #define SK_API __attribute__((visibility("default")))
         #endif
     #else
-        #define SK_API __attribute__((visibility("default")))
+        #define SK_API
     #endif
-#else
-    #define SK_API
 #endif
 
 //////////////////////////////////////////////////////////////////////