Distinguish between JANET_API and JANET_EXPORT

One is a way to export symbols, the other a way to reference
API functions. Also include prebuilt dlljanet.dll and dlljanet.lib
for windows to save people the trouble of compiling janet.c themselves.

build_win.bat

@@ -64,6 +64,10 @@ rc /nologo /fobuild\janet_win.res janet_win.rc
 %JANET_LINK% /out:janet.exe build\janet.obj build\shell.obj build\janet_win.res
 @if errorlevel 1 goto :BUILDFAIL
 
+@rem Build dynamic library (dlljanet.dll)
+%JANET_LINK% /DLL /out:build\dlljanet.dll build\janet.obj
+@if errorlevel 1 goto :BUILDFAIL
+
 @rem Build static library (libjanet.lib)
 %JANET_LINK_STATIC% /out:build\libjanet.lib build\janet.obj
 @if errorlevel 1 goto :BUILDFAIL
@@ -122,6 +126,8 @@ copy janet.def dist\janet.def
 janet.exe tools\patch-header.janet src\include\janet.h src\conf\janetconf.h build\janet.h
 copy build\janet.h dist\janet.h
 copy build\libjanet.lib dist\libjanet.lib
+copy build\dlljanet.dll dist\dlljanet.dll
+copy build\dlljanet.lib dist\dlljanet.lib
 
 @rem Create installer
 janet.exe -e "(->> janet/version (peg/match ''(* :d+ `.` :d+ `.` :d+)) first print)" > build\version.txt

src/include/janet.h

@@ -235,6 +235,15 @@ extern "C" {
 #endif
 
 /* How to export symbols */
+#ifndef JANET_EXPORT
+#ifdef JANET_WINDOWS
+#define JANET_EXPORT __declspec(dllexport)
+#else
+#define JANET_EXPORT __attribute__((visibility ("default")))
+#endif
+#endif
+
+/* How declare API functions */
 #ifndef JANET_API
 #ifdef JANET_WINDOWS
 #ifdef JANET_DLL_IMPORT
@@ -734,6 +743,7 @@ JANET_API Janet janet_wrap_integer(int32_t x);
         ? janet_nanbox_isnumber(x) \
         : janet_nanbox_checkauxtype((x), (t)))
 
+/* Use JANET_API so that modules will use a local version of these functions if possible */
 JANET_API void *janet_nanbox_to_pointer(Janet x);
 JANET_API Janet janet_nanbox_from_pointer(void *p, uint64_t tagmask);
 JANET_API Janet janet_nanbox_from_cpointer(const void *p, uint64_t tagmask);
@@ -1952,10 +1962,10 @@ JANET_API void janet_register(const char *name, JanetCFunction cfun);
 #endif
 #ifndef JANET_ENTRY_NAME
 #define JANET_MODULE_ENTRY \
-    JANET_MODULE_PREFIX JANET_API JanetBuildConfig _janet_mod_config(void) { \
+    JANET_MODULE_PREFIX JANET_EXPORT JanetBuildConfig _janet_mod_config(void) { \
         return janet_config_current(); \
     } \
-    JANET_MODULE_PREFIX JANET_API void _janet_init
+    JANET_MODULE_PREFIX JANET_EXPORT void _janet_init
 #else
 #define JANET_MODULE_ENTRY JANET_MODULE_PREFIX JANET_API void JANET_ENTRY_NAME
 #endif

tools/msi/janet.wxs

@@ -132,6 +132,12 @@
             <Component Directory="CDir">
                 <File Source="dist\libjanet.lib"/>
             </Component>
+            <Component Directory="CDir">
+                <File Source="dist\dlljanet.dll"/>
+            </Component>
+            <Component Directory="CDir">
+                <File Source="dist\dlljanet.lib"/>
+            </Component>
 
             <Component Id="LibraryComponent" Directory="LibraryDir" Guid="3860e981-5f94-4002-b5d5-2d9ec0d2792d" KeyPath="yes">
                 <RemoveFolder Id="RemoveLibraryDir" On="uninstall" />