Fix build of userboot.so

Since it's not possible to unset a variable easily, create a new
variable 'PIC' to signal that we are creating a shared object that we
want to install. defs.mk refains from defining NO_PIC and ITNERALLIB
when PIC is defined. This unbreaks userboot.so building.

stand/defs.mk

@@ -10,9 +10,11 @@ __BOOT_DEFS_MK__=${MFILE}
 MK_CTF=		no
 MK_SSP=		no
 MK_PROFILE=	no
-NO_PIC=
 MAN=
+.if !defined(PIC)
+NO_PIC=
 INTERNALLIB=
+.endif
 
 BOOTSRC=	${SRCTOP}/stand
 EFISRC=		${BOOTSRC}/efi

stand/userboot/userboot/Makefile

@@ -4,6 +4,7 @@ LOADER_MSDOS_SUPPORT?=	yes
 LOADER_UFS_SUPPORT?=	yes
 LOADER_CD9660_SUPPORT?=	no
 LOADER_EXT2FS_SUPPORT?=	no
+PIC=yes
 
 .include <bsd.init.mk>