diff --git a/LibC/assert.h b/LibC/assert.h
index 36be4b57f0..9420363bba 100644
--- a/LibC/assert.h
+++ b/LibC/assert.h
@@ -4,7 +4,7 @@
 
 __BEGIN_DECLS
 
-[[noreturn]] void __assertion_failed(const char* msg, const char* file, unsigned line, const char* func);
+__attribute__((noreturn)) void __assertion_failed(const char* msg, const char* file, unsigned line, const char* func);
 
 #define assert(expr) ((expr) ? (void)0 : __assertion_failed(#expr, __FILE__, __LINE__, __PRETTY_FUNCTION__))
 #define CRASH() do { asm volatile("ud2"); } while(0)
diff --git a/LibC/ctype.h b/LibC/ctype.h
index f3ac9d2218..41178f5cb4 100644
--- a/LibC/ctype.h
+++ b/LibC/ctype.h
@@ -4,41 +4,41 @@
 
 __BEGIN_DECLS
 
-[[gnu::always_inline]] inline int isascii(int ch)
+ALWAYS_INLINE int isascii(int ch)
 {
     return (ch & ~0x7f) == 0;
 }
 
-[[gnu::always_inline]] inline int isspace(int ch)
+ALWAYS_INLINE int isspace(int ch)
 {
     return ch == ' ' || ch == '\f' || ch == '\n' || ch == '\r' || ch == '\t' || ch == '\v';
 }
 
-[[gnu::always_inline]] inline int islower(int c)
+ALWAYS_INLINE int islower(int c)
 {
     return c >= 'a' && c <= 'z';
 }
 
-[[gnu::always_inline]] inline int isupper(int c)
+ALWAYS_INLINE int isupper(int c)
 {
     return c >= 'A' && c <= 'Z';
 }
 
-[[gnu::always_inline]] inline int tolower(int c)
+ALWAYS_INLINE int tolower(int c)
 {
     if (isupper(c))
         return c | 0x20;
     return c;
 }
 
-[[gnu::always_inline]] inline int toupper(int c)
+ALWAYS_INLINE int toupper(int c)
 {
     if (islower(c))
         return c & ~0x20;
     return c;
 }
 
-[[gnu::always_inline]] inline int isdigit(int c)
+ALWAYS_INLINE int isdigit(int c)
 {
     return c >= '0' && c <= '9';
 }
diff --git a/LibC/stdlib.h b/LibC/stdlib.h
index 064ce160f6..efca85b68c 100644
--- a/LibC/stdlib.h
+++ b/LibC/stdlib.h
@@ -9,16 +9,16 @@ __BEGIN_DECLS
 #define EXIT_FAILURE 1
 #define MB_CUR_MAX 1
 
-[[gnu::malloc, gnu::alloc_size(1)]] void* malloc(size_t);
-[[gnu::malloc, gnu::alloc_size(1, 2)]] void* calloc(size_t nmemb, size_t);
+__attribute__((malloc)) __attribute__((alloc_size(1))) void* malloc(size_t);
+__attribute__((malloc)) __attribute__((alloc_size(1, 2))) void* calloc(size_t nmemb, size_t);
 void free(void*);
 void* realloc(void *ptr, size_t);
 char* getenv(const char* name);
 int atoi(const char*);
 long atol(const char*);
 void qsort(void* base, size_t nmemb, size_t size, int (*compar)(const void *, const void *));
-[[noreturn]] void exit(int status);
-[[noreturn]] void abort();
+__attribute__((noreturn)) void exit(int status);
+__attribute__((noreturn)) void abort();
 char* ptsname(int fd);
 int ptsname_r(int fd, char* buffer, size_t);
 int abs(int);
diff --git a/LibC/sys/cdefs.h b/LibC/sys/cdefs.h
index 9fcd9b1682..0d558557fd 100644
--- a/LibC/sys/cdefs.h
+++ b/LibC/sys/cdefs.h
@@ -2,6 +2,8 @@
 
 #define _POSIX_VERSION 200809L
 
+#define ALWAYS_INLINE inline __attribute__((always_inline))
+
 #ifdef __cplusplus
 #define __BEGIN_DECLS extern "C" {
 #define __END_DECLS }