Install the 32-bit compat sanitizer libraries.

The lib32 build was already building the i386 version of
the clang sanitizers (libclang_rt) but they were not being
installed.  This enables the installation.

MK_TOOLCHAIN=no was originally added to the install make
environment to disable includes so that NO_INCS could be
removed.  The MK_TOOLCHAIN in bsd.incs.mk was subsequently
renamed to MK_INCLUDES, but bsd.lib.mk doesn't even include
bsd.incs.mk when LIBRARIES_ONLY is defined which the install
make environment for compat libs now defines.  However,
setting MK_TOOLCHAIN=no forced MK_CLANG=no which disabled
libclang_rt during the install32 phase.  Remove MK_TOOLCHAIN=no
since LIBRARIES_ONLY is now sufficient.

Since the libcompat environment overrides both LIBDIR and
SHLIBDIR, libclang_rt/Makefile.inc has to set both variables
to force the libraries to be installed to the location
expected by the compiler.

Reviewed by:	bdrewery, dim
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D16574

Makefile.libcompat

@@ -126,7 +126,7 @@ LIBCOMPATWMAKE+=	${LIBCOMPATWMAKEENV} ${MAKE} ${LIBCOMPATWMAKEFLAGS} \
 			MAKEOBJDIRPREFIX= \
 			MK_MAN=no MK_HTML=no
 LIBCOMPATIMAKE+=	${LIBCOMPATWMAKE:NINSTALL=*:NDESTDIR=*} \
-			MK_TOOLCHAIN=no ${IMAKE_INSTALL} \
+			${IMAKE_INSTALL} \
 			-DLIBRARIES_ONLY
 
 _LC_LIBDIRS.yes=		lib

lib/libclang_rt/Makefile.inc

@@ -16,6 +16,7 @@ CRTSRC=		${SRCTOP}/contrib/compiler-rt
 
 CLANGDIR=	/usr/lib/clang/6.0.1
 LIBDIR=		${CLANGDIR}/lib/freebsd
+SHLIBDIR=	${LIBDIR}
 
 NO_PIC=
 MK_PROFILE=	no