scons: build osmesa swrast and gallium

This patch makes it possible to build classic osmesa/swrast on windows
again. It was removed in commit 69db422218.
Although there is a gallium version of osmesa now, the swrast version
still has more features lacking in llvmpipe, e.g. anisotropic filtering.

Tested-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
[Emil Velikov: remove trailing whitespace]
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>

src/mesa/drivers/SConscript

@@ -1,5 +1,7 @@
 Import('*')
 
+SConscript('osmesa/SConscript')
+
 if env['x11']:
     SConscript('x11/SConscript')
 

src/mesa/drivers/osmesa/SConscript

@@ -0,0 +1,40 @@
+Import('*')
+
+env = env.Clone()
+
+env.Prepend(CPPPATH = [
+    '#src',
+    '#src/mapi',
+    '#src/mesa',
+    Dir('../../../mapi'), # src/mapi build path for python-generated GL API files/headers
+])
+
+env.Prepend(LIBS = [
+    mesautil,
+    glapi,
+    compiler,
+    mesa,
+    glsl,
+])
+
+sources = [
+    'osmesa.c',
+]
+
+if env['platform'] == 'windows':
+    env.AppendUnique(CPPDEFINES = [
+        '_GDI32_', # prevent wgl* being declared __declspec(dllimport)
+        'BUILD_GL32', # declare gl* as __declspec(dllexport) in Mesa headers
+    ])
+    if not env['gles']:
+        # prevent _glapi_* from being declared __declspec(dllimport)
+        env.Append(CPPDEFINES = ['_GLAPI_NO_EXPORTS'])
+
+    sources += ['osmesa.def']
+
+osmesa = env.SharedLibrary(
+    target ='osmesa',
+    source = sources,
+)
+
+env.Alias('osmesa', osmesa)

src/mesa/drivers/osmesa/osmesa.def

@@ -0,0 +1,15 @@
+;DESCRIPTION 'Mesa OSMesa lib for Win32'
+VERSION 4.1
+
+EXPORTS
+	OSMesaColorClamp
+	OSMesaCreateContext
+	OSMesaCreateContextExt
+	OSMesaDestroyContext
+	OSMesaMakeCurrent
+	OSMesaGetCurrentContext
+	OSMesaPixelStore
+	OSMesaGetIntegerv
+	OSMesaGetDepthBuffer
+	OSMesaGetColorBuffer
+	OSMesaGetProcAddress