libc: Add abs(), labs() and llabs()

Just needed to alias them to GCC builtins.

libs/libc/include/stdlib.h

@@ -65,6 +65,15 @@ extern "C"
     /* Seeds the random number generator with the specified seed. */
     void srand(unsigned int seed);
 
+    /* Returns the absolute value of an integer. */
+    int abs(int val);
+
+    /* Returns the absolute value of an integer. */
+    long labs(long val);
+
+    /* Returns the absolute value of an integer. */
+    long long llabs(long long val);
+
 #ifdef __cplusplus
 }
 #endif

libs/libc/src/stdlib.cpp

@@ -63,4 +63,19 @@ extern "C"
         syscall(SYS_exit, status);
         __lc_unreachable();
     }
+
+    int abs(int val)
+    {
+        return __builtin_abs(val);
+    }
+
+    long labs(long val)
+    {
+        return __builtin_labs(val);
+    }
+
+    long long llabs(long long val)
+    {
+        return __builtin_llabs(val);
+    }
 }