_Really_, _Really_ fix buildworld by moving the conditionals down, fixing some

typos, and fixing the dependency when MK_LIBCPLUSPLUS != no

- `:D` operator evaluation is immediate, i.e. like .if defined(..). So r283159
  was in effect a no-op commit.
- Fix dependency in MK_LIBCPLUSPLUS case in two ways:
-- lib/libc++ was the wrong dependency. It should have been libcxxrt.
-- lib/libc++ was missing __L, so again it was depending on the directory, not
   the relevant .PHONY target.

Tested with: make tinderbox (amd64, arm, sparc64) and JFLAG=-j16
In collaboration with: bdrewery, imp, peter
BIG pointyhat to: ngie (for trying to commit things at 6am while staying up all
                        night working on other tasks)

Makefile.inc1

@@ -1744,16 +1744,6 @@ _generic_libs+= ${_DIR}
 
 lib/libopie__L lib/libtacplus__L: lib/libmd__L
 
-lib/libproc__L: \
-    ${_cddl_lib_libctf:D${_cddl_lib_libctf}__L} lib/libelf__L lib/librtld_db__L lib/libutil__L
-.if ${MK_CXX} != "no"
-.if ${MK_LIBCPLUSPLUS} != "no"
-lib/libproc__L: lib/libc++
-.else
-lib/libproc__L: gnu/lib/libsupc++__L
-.endif
-.endif
-
 .if ${MK_CDDL} != "no"
 _cddl_lib_libumem= cddl/lib/libumem
 _cddl_lib_libnvpair= cddl/lib/libnvpair
@@ -1846,6 +1836,16 @@ _lib_libypclnt=	lib/libypclnt
 lib/libradius__L: lib/libmd__L
 .endif
 
+lib/libproc__L: \
+    ${_cddl_lib_libctf:D${_cddl_lib_libctf}__L} lib/libelf__L lib/librtld_db__L lib/libutil__L
+.if ${MK_CXX} != "no"
+.if ${MK_LIBCPLUSPLUS} != "no"
+lib/libproc__L: lib/libcxxrt__L
+.else # This implies MK_GNUCXX != "no"; see lib/libproc
+lib/libproc__L: gnu/lib/libsupc++__L
+.endif
+.endif
+
 gnu/lib/libdialog__L: lib/msun__L lib/ncurses/ncursesw__L
 
 .for _lib in ${_prereq_libs}