[m-rev.] for review: Disable detection of libhwloc by default.

[Peter Wang]

libhwloc is only used to support thread pinning in low-level C grades,
an experimental (and IMHO dubious) feature that needs to be manually
enabled via MERCURY_OPTIONS. On Linux, we also support thread pinning
without libhwloc. In fact, when I tested it, thread pinning ONLY works
without using libhwloc, so some code has probably bit-rotted.

configure.ac:
    Disable detection of libhwloc by default so we don't try to use it
    just because it happens to be installed.
---
 configure.ac | 20 +++++++-------------
 1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/configure.ac b/configure.ac
index f7f2eb77f..012033607 100644
--- a/configure.ac
+++ b/configure.ac
@@ -5201,43 +5201,37 @@ AC_SUBST(USE_MSVCRT)
 #
 # Check for readline
 #
 
 MERCURY_CHECK_READLINE
 
 #-----------------------------------------------------------------------------#
 #
 # Check for libhwloc, http://www.open-mpi.org/projects/hwloc/
 #
+
 PKG_PROG_PKG_CONFIG
 
 AC_ARG_WITH([hwloc],
-    [AS_HELP_STRING([--without-hwloc],
-        [Do not use libhwloc to detect the processors available.])],
-    [],
-    [with_hwloc=check])
+    AS_HELP_STRING([--with-hwloc],
+        [Use libhwloc in support of thread pinning (developers only)]),
+    [with_hwloc="$withval"],
+    [with_hwloc="no"])
 
-if test "$with_hwloc" != "no"; then
+if test "$with_hwloc" = "yes"
+then
     PKG_CHECK_MODULES(libhwloc, hwloc >= 1.1,
         [
             AC_DEFINE(MR_HAVE_HWLOC)
             hwloc_static_libs="`pkg-config --libs --static hwloc`"
         ],
         [
-            case "$LIBGRADES" in
-                $BEST_LLDS_BASE_GRADE.par.gc*)
-                    MERCURY_MSG(["Warning: libhwloc not found, thread pinning in"])
-                    MERCURY_MSG(["low-level C parallel grades may be less accurate."])
-                    ;;
-                *)
-                    ;;
-            esac
             hwloc_static_libs=""
         ])
 else
     libhwloc_LIBS=""
     libhwloc_CFLAGS=""
     hwloc_static_libs=""
 fi
 
 HWLOC_LIBS="$libhwloc_LIBS"
 HWLOC_CFLAGS="$libhwloc_CFLAGS"
-- 
2.17.0