AK: We can't use std::initializer_list in LibC builds.

The LibC build is a bit complicated, since the toolchain depends on it.
During the toolchain bootstrap, after we've built parts of GCC, we have
to stop and build Serenity's LibC, so that the rest of GCC can use it.

This means that during that specific LibC build, we don't yet have access
to things like std::initializer_list.

For now we solve this by defining SERENITY_LIBC_BUILD during the LibC
build and excluding the Vector/initializer_list support inside LibC.

AK/Vector.h

@@ -3,7 +3,13 @@
 #include <AK/Assertions.h>
 #include <AK/StdLibExtras.h>
 #include <AK/kmalloc.h>
+
+// NOTE: We can't include <initializer_list> during the toolchain bootstrap,
+//       since it's part of libstdc++, and libstdc++ depends on LibC.
+//       For this reason, we don't support Vector(initializer_list) in LibC.
+#ifndef SERENITY_LIBC_BUILD
 #include <initializer_list>
+#endif
 
 #ifndef __serenity__
 #include <new>
@@ -65,12 +71,14 @@ public:
         clear();
     }
 
+#ifndef SERENITY_LIBC_BUILD
     Vector(std::initializer_list<T> list)
     {
         ensure_capacity(list.size());
         for (auto& item : list)
             unchecked_append(item);
     }
+#endif
 
     Vector(Vector&& other)
         : m_size(other.m_size)

LibC/Makefile

@@ -58,7 +58,7 @@ ASM_OBJS = setjmp.ao crti.ao crtn.ao
 CPP_OBJS = $(AK_OBJS) $(WIDGETS_OBJS) $(LIBC_OBJS)
 
 LIBRARY = libc.a
-DEFINES += -DUSERLAND
+DEFINES += -DUSERLAND -DSERENITY_LIBC_BUILD
 
 all: $(LIBRARY) startfiles