Revert "Build: Include headers from LibC, LibM, and LibPthread with -isystem"

This reverts commit c1eb744ff0.

Userland/functrace.cpp

@@ -33,6 +33,7 @@
 #include <AK/StringBuilder.h>
 #include <AK/kmalloc.h>
 #include <Kernel/Syscall.h>
+#include <LibC/sys/arch/i386/regs.h>
 #include <LibCore/File.h>
 #include <LibDebug/DebugSession.h>
 #include <LibELF/Image.h>
@@ -43,7 +44,6 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <sys/arch/i386/regs.h>
 #include <unistd.h>
 
 static int usage()

Userland/strace.cpp

@@ -28,11 +28,11 @@
 #include <AK/LogStream.h>
 #include <AK/Types.h>
 #include <Kernel/Syscall.h>
+#include <LibC/sys/arch/i386/regs.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <sys/arch/i386/regs.h>
 #include <sys/ptrace.h>
 #include <sys/wait.h>
 #include <unistd.h>

Userland/test-crypto.cpp

@@ -24,6 +24,7 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <LibC/limits.h>
 #include <LibCore/ArgsParser.h>
 #include <LibCore/EventLoop.h>
 #include <LibCore/File.h>
@@ -36,7 +37,6 @@
 #include <LibCrypto/PK/RSA.h>
 #include <LibLine/Editor.h>
 #include <LibTLS/TLSv12.h>
-#include <limits.h>
 #include <stdio.h>
 #include <time.h>