Misc: Modify function attributes

- Remove the const function attribute from get_time_*(), since the
   functions they call that actually get the time probably access global
   variables or have other behaviors unacceptable for const functions.

 - Change the const function attribute on win_has_frame() to pure, as it
   accesses memory its parameter points to, which is invalid for a const
   function.

src/common.h

@@ -1475,7 +1475,7 @@ timespec_subtract(struct timespec *result,
 /**
  * Get current time in struct timeval.
  */
-static inline struct timeval __attribute__((const))
+static inline struct timeval
 get_time_timeval(void) {
   struct timeval tv = { 0, 0 };
 
@@ -1490,7 +1490,7 @@ get_time_timeval(void) {
  *
  * Note its starting time is unspecified.
  */
-static inline struct timespec __attribute__((const))
+static inline struct timespec
 get_time_timespec(void) {
   struct timespec tm = { 0, 0 };
 

src/compton.h

@@ -500,7 +500,7 @@ update_reg_ignore_expire(session_t *ps, const win *w) {
 /**
  * Check whether a window has WM frames.
  */
-static inline bool __attribute__((const))
+static inline bool __attribute__((pure))
 win_has_frame(const win *w) {
   return w->a.border_width
     || w->frame_extents.top || w->frame_extents.left