Also link in math library in static build

It's included by default in dynamic builds so we need to make sure it
isn't lost when switching to static.

cmake/StaticBuild.cmake

@@ -139,7 +139,7 @@ if(BUILD_STATIC_GCC)
     # these things again
     set(STATIC_BASE_LIBRARIES "${STATIC_BASE_LIBRARIES} -lmingw32 -lgcc_eh -lgcc -lmoldname -lmingwex -lmsvcrt")
   else()
-    set(STATIC_BASE_LIBRARIES "${STATIC_BASE_LIBRARIES} -lgcc -lgcc_eh -lc")
+    set(STATIC_BASE_LIBRARIES "${STATIC_BASE_LIBRARIES} -lm -lgcc -lgcc_eh -lc")
   endif()
   set(CMAKE_C_LINK_EXECUTABLE "${CMAKE_C_LINK_EXECUTABLE} ${STATIC_BASE_LIBRARIES}")
   set(CMAKE_CXX_LINK_EXECUTABLE "${CMAKE_CXX_LINK_EXECUTABLE} -Wl,-Bstatic -lstdc++ -Wl,-Bdynamic ${STATIC_BASE_LIBRARIES}")