[m-rev.] for review: Make link-time optimisation with gcc work.

[Peter Wang]

configure.ac:
    Add -flto to LINK_SHARED_OBJ and LINK_SHARED_OBJ_SH commands
    when LTO is enabled with gcc.

    Search for and use LTO-aware gcc-ar, gcc-ranlib and gcc-nm
    programs in place of the normal tools.

diff --git a/configure.ac b/configure.ac
index 3e7e10c09..6dbee8860 100644
--- a/configure.ac
+++ b/configure.ac
@@ -5348,7 +5348,19 @@ if test "$mercury_cv_lto" = "yes"; then
             CFLAGS_FOR_LTO="-GL"
             LDFLAGS_FOR_LTO="-LTCG"
             ;;
-        gcc*|clang*)
+        gcc*)
+            CFLAGS_FOR_LTO="-flto"
+            LDFLAGS_FOR_LTO="-flto"
+            LINK_SHARED_OBJ="$LINK_SHARED_OBJ -flto"
+            LINK_SHARED_OBJ_SH="$LINK_SHARED_OBJ_SH -flto"
+            AC_CHECK_TOOL([GCC_AR], [gcc-ar], [])
+            AC_CHECK_TOOL([GCC_RANLIB], [gcc-ranlib], [])
+            AC_CHECK_TOOL([GCC_NM], [gcc-nm], [])
+            AR=${GCC_AR:-$AR}
+            RANLIB=${GCC_RANLIB:-$RANLIB}
+            NM=${GCC_NM:-$NM}
+            ;;
+        clang*)
             CFLAGS_FOR_LTO="-flto"
             LDFLAGS_FOR_LTO="-flto"
             ;;
-- 
2.25.0