svga/drm: Optionally resolve calls to powf during link-time

When linked with certain builds of libstdc++, it appears like powf is resolved
by a symbol in that library. Other builds of libstdc++ doesn't contain that
symbol resulting in a linker / loader error. Optionally
resolve that symbol and replace it with calls to logf and expf.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>

src/gallium/targets/dri-vmwgfx/Makefile

@@ -12,6 +12,7 @@ PIPE_DRIVERS = \
 
 C_SOURCES = \
 	target.c \
+	vmw_powf.c \
 	$(COMMON_GALLIUM_SOURCES)
 
 DRIVER_DEFINES = \

src/gallium/targets/dri-vmwgfx/vmw_powf.c

@@ -0,0 +1,17 @@
+/**
+ * Powf may leave an unresolved symbol pointing to a libstdc++.so powf.
+ * However, not all libstdc++.so include this function, so optionally
+ * replace the powf function with calls to expf and logf.
+ */
+
+#ifdef VMW_RESOLVE_POWF
+
+extern float expf(float x);
+extern float logf(float x);
+extern float powf(float x, float y);
+
+float powf(float x, float y) {
+    return expf(logf(x)*y);
+}
+
+#endif