use [[gnu::pure]] instead of gcc_pure

This is semi-standard and doesn't require the util/Compiler.h header.

src/time/ClockCache.hxx

@@ -47,7 +47,7 @@ public:
 	ClockCache(const ClockCache &) = delete;
 	ClockCache &operator=(const ClockCache &) = delete;
 
-	gcc_pure
+	[[gnu::pure]]
 	const auto &now() const noexcept {
 		if (value <= value_type())
 			value = Clock::now();

src/time/Convert.cxx

@@ -72,7 +72,7 @@ LocalTime(std::chrono::system_clock::time_point tp)
 /**
  * Determine the time zone offset in a portable way.
  */
-gcc_const
+[[gnu::const]]
 static time_t
 GetTimeZoneOffset() noexcept
 {

src/time/Convert.hxx

@@ -33,8 +33,6 @@
 #ifndef TIME_CONVERT_HXX
 #define TIME_CONVERT_HXX
 
-#include "util/Compiler.h"
-
 #include <chrono>
 
 /**
@@ -56,18 +54,18 @@ LocalTime(std::chrono::system_clock::time_point tp);
 /**
  * Convert a UTC-based "struct tm" to a UTC-based time point.
  */
-gcc_pure
+[[gnu::pure]]
 std::chrono::system_clock::time_point
 TimeGm(struct tm &tm) noexcept;
 
 /**
  * Convert a local "struct tm" to a UTC-based time point.
  */
-gcc_pure
+[[gnu::pure]]
 std::chrono::system_clock::time_point
 MakeTime(struct tm &tm) noexcept;
 
-gcc_pure
+[[gnu::pure]]
 std::chrono::steady_clock::duration
 ToSteadyClockDuration(const struct timeval &tv) noexcept;
 

src/time/ISO8601.hxx

@@ -33,8 +33,6 @@
 #ifndef TIME_ISO8601_HXX
 #define TIME_ISO8601_HXX
 
-#include "util/Compiler.h"
-
 #include <chrono>
 #include <cstddef>
 #include <utility>
@@ -42,11 +40,11 @@
 struct tm;
 template<size_t CAPACITY> class StringBuffer;
 
-gcc_pure
+[[gnu::pure]]
 StringBuffer<64>
 FormatISO8601(const struct tm &tm) noexcept;
 
-gcc_pure
+[[gnu::pure]]
 StringBuffer<64>
 FormatISO8601(std::chrono::system_clock::time_point tp);
 

src/time/Math.hxx

@@ -32,8 +32,6 @@
 
 #pragma once
 
-#include "util/Compiler.h"
-
 #include <chrono>
 
 struct tm;
@@ -42,7 +40,7 @@ struct tm;
  * Calculates the preceding midnight time point in the current time
  * zone.
  */
-gcc_const
+[[gnu::const]]
 std::chrono::system_clock::time_point
 PrecedingMidnightLocal(std::chrono::system_clock::time_point t) noexcept;