LibC: Move `_abort` next to `abort`

It should be now the only user of it, and it is more logical to have it
in `stdlib.h` than in `assert.h`

Userland/Libraries/LibC/assert.cpp

@@ -33,9 +33,3 @@ void __assertion_failed(const char* msg)
     abort();
 }
 }
-
-void _abort()
-{
-    asm volatile("ud2");
-    __builtin_unreachable();
-}

Userland/Libraries/LibC/assert.h

@@ -23,8 +23,6 @@ __attribute__((noreturn)) void __assertion_failed(const char* msg);
 #    define assert(expr) ((void)(0))
 #endif
 
-__attribute__((noreturn)) void _abort();
-
 #ifndef __cplusplus
 #    define static_assert _Static_assert
 #endif

Userland/Libraries/LibC/stdlib.cpp

@@ -209,6 +209,12 @@ int atexit(void (*handler)())
     return __cxa_atexit(__atexit_to_cxa_atexit, (void*)handler, nullptr);
 }
 
+void _abort()
+{
+    asm volatile("ud2");
+    __builtin_unreachable();
+}
+
 void abort()
 {
     // For starters, send ourselves a SIGABRT.

Userland/Libraries/LibC/stdlib.h

@@ -16,6 +16,8 @@ __BEGIN_DECLS
 #define EXIT_FAILURE 1
 #define MB_CUR_MAX 4
 
+__attribute__((noreturn)) void _abort();
+
 __attribute__((malloc)) __attribute__((alloc_size(1))) void* malloc(size_t);
 __attribute__((malloc)) __attribute__((alloc_size(1, 2))) void* calloc(size_t nmemb, size_t);
 size_t malloc_size(void*);