Mark DllMain and similar exports as private.

dlls/advpack/advpack.spec

diff --git a/dlls/advpack/advpack.spec b/dlls/advpack/advpack.spec
index da09523..3a193f0 100644
--- a/dlls/advpack/advpack.spec
+++ b/dlls/advpack/advpack.spec
@@ -3,7 +3,7 @@
 @ stub CloseINFEngine
 @ stdcall DelNode(str long)
 @ stdcall DelNodeRunDLL32(ptr ptr str long)
-@ stdcall DllMain(long long ptr)
+@ stdcall -private DllMain(long long ptr)
 @ stdcall DoInfInstall(ptr)
 @ stdcall ExecuteCab(ptr ptr ptr)
 @ stub ExtractFiles

dlls/dciman32/dciman32.spec

diff --git a/dlls/dciman32/dciman32.spec b/dlls/dciman32/dciman32.spec
index 5a7aa7a..ee235d0 100644
--- a/dlls/dciman32/dciman32.spec
+++ b/dlls/dciman32/dciman32.spec
@@ -11,7 +11,7 @@
 @ stub    DCISetClipList
 @ stub    DCISetDestination
 @ stub    DCISetSrcDestClip
-@ stdcall DllEntryPoint(long long ptr) DllMain
+@ stdcall -private DllEntryPoint(long long ptr) DllMain
 @ stub    GetDCRegionData
 @ stub    GetWindowRegionData
 @ stub    WinWatchClose

dlls/itss/itss.spec

diff --git a/dlls/itss/itss.spec b/dlls/itss/itss.spec
index edc6242..a5e0c57 100644
--- a/dlls/itss/itss.spec
+++ b/dlls/itss/itss.spec
@@ -1,6 +1,6 @@
 @ stdcall -private DllCanUnloadNow()
 @ stdcall -private DllGetClassObject(ptr ptr ptr)
 @ stub DllInstall
-@ stdcall DllMain(long long ptr)
+@ stdcall -private DllMain(long long ptr)
 @ stdcall -private DllRegisterServer()
 @ stub DllUnregisterServer

dlls/msimg32/msimg32.spec

diff --git a/dlls/msimg32/msimg32.spec b/dlls/msimg32/msimg32.spec
index 7730846..76b5075 100644
--- a/dlls/msimg32/msimg32.spec
+++ b/dlls/msimg32/msimg32.spec
@@ -1,5 +1,5 @@
 @ stdcall AlphaBlend(long long long long long long long long long long long) gdi32.GdiAlphaBlend
-@ stdcall DllInitialize(long long ptr) DllMain
+@ stdcall -private DllInitialize(long long ptr) DllMain
 @ stdcall GradientFill(long ptr long ptr long long) gdi32.GdiGradientFill
 @ stdcall TransparentBlt(long long long long long long long long long long long) gdi32.GdiTransparentBlt
 @ stdcall vSetDdrawflag()