x86: Import the glibc memset implementation

The new implementation is about twice as fast as the old. This is from
glibc-2.14, sysdeps/i386/memset.c.

Signed-off-by: Gabe Black <gabeblack@chromium.org>
diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index eb5fa10..90f3283 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -38,6 +38,7 @@
 COBJS-$(CONFIG_PCI) += pci.o
 COBJS-$(CONFIG_PCI) += pci_type1.o
 COBJS-$(CONFIG_SYS_X86_REALMODE)	+= realmode.o
+COBJS-y	+= string.o
 COBJS-$(CONFIG_SYS_X86_ISR_TIMER)	+= timer.o
 COBJS-$(CONFIG_VIDEO)	+= video_bios.o
 COBJS-$(CONFIG_VIDEO)	+= video.o