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

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

src/system/Error.hxx

@@ -30,8 +30,6 @@
 #ifndef SYSTEM_ERROR_HXX
 #define SYSTEM_ERROR_HXX
 
-#include "util/Compiler.h"
-
 #include <system_error> // IWYU pragma: export
 #include <utility>
 
@@ -160,7 +158,7 @@ FormatFileNotFound(const char *fmt, Args&&... args) noexcept
 #endif
 }
 
-gcc_pure
+[[gnu::pure]]
 inline bool
 IsErrno(const std::system_error &e, int code) noexcept
 {
@@ -168,7 +166,7 @@ IsErrno(const std::system_error &e, int code) noexcept
 		e.code().value() == code;
 }
 
-gcc_pure
+[[gnu::pure]]
 static inline bool
 IsFileNotFound(const std::system_error &e) noexcept
 {
@@ -180,7 +178,7 @@ IsFileNotFound(const std::system_error &e) noexcept
 #endif
 }
 
-gcc_pure
+[[gnu::pure]]
 static inline bool
 IsPathNotFound(const std::system_error &e) noexcept
 {
@@ -192,7 +190,7 @@ IsPathNotFound(const std::system_error &e) noexcept
 #endif
 }
 
-gcc_pure
+[[gnu::pure]]
 static inline bool
 IsAccessDenied(const std::system_error &e) noexcept
 {

src/system/KernelVersion.cxx

@@ -35,7 +35,7 @@
 #include <sys/utsname.h>
 #include <stdio.h>
 
-gcc_const
+[[gnu::const]]
 static KernelVersionCode
 GetKernelVersionCode() noexcept
 {

src/system/KernelVersion.hxx

@@ -32,8 +32,6 @@
 
 #pragma once
 
-#include "util/Compiler.h"
-
 class KernelVersionCode {
 	unsigned value = 0;
 
@@ -53,6 +51,6 @@ public:
 /**
  * Is the currently running Linux kernel at least the given version?
  */
-gcc_const
+[[gnu::const]]
 bool
 IsKernelVersionOrNewer(KernelVersionCode v) noexcept;