Rename DLLEXPORT AND STDCALL

This CL renames DLLEXPORT to FPDF_EXPORT and STDCALL to FPDF_CALLCONV to
be more PDFium specific.

This is split off of https://pdfium-review.googlesource.com/c/8970 by
Felix Kauselmann.

Bug: pdfium:825
Change-Id: I0aea9d43f1714b1e10e935c4a7eea685a5ad8998
Reviewed-on: https://pdfium-review.googlesource.com/10610
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>
diff --git a/fpdfsdk/fpdf_ext.cpp b/fpdfsdk/fpdf_ext.cpp
index f598835..2284453 100644
--- a/fpdfsdk/fpdf_ext.cpp
+++ b/fpdfsdk/fpdf_ext.cpp
@@ -37,7 +37,7 @@
   return true;
 }
 
-DLLEXPORT FPDF_BOOL STDCALL
+FPDF_EXPORT FPDF_BOOL FPDF_CALLCONV
 FSDK_SetUnSpObjProcessHandler(UNSUPPORT_INFO* unsp_info) {
   if (!unsp_info || unsp_info->version != 1)
     return false;
@@ -169,7 +169,7 @@
 #endif  // PDF_ENABLE_XFA
 }
 
-DLLEXPORT int STDCALL FPDFDoc_GetPageMode(FPDF_DOCUMENT document) {
+FPDF_EXPORT int FPDF_CALLCONV FPDFDoc_GetPageMode(FPDF_DOCUMENT document) {
   CPDF_Document* pDoc = CPDFDocumentFromFPDFDocument(document);
   if (!pDoc)
     return PAGEMODE_UNKNOWN;