make --enable-gdb-index the default for debug builds, if supported

Currently only done on Linux, I'm not sure about the status on other platforms,
feel free to add your platform.
https://lists.freedesktop.org/archives/libreoffice/2018-June/080437.html
https://lists.freedesktop.org/archives/libreoffice/2018-July/080484.html

Change-Id: I5997f54e530c8078250eb7c116cb6bd2604e7925
Reviewed-on: https://gerrit.libreoffice.org/65424
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

configure.ac

@@ -553,6 +553,7 @@ test_cups=yes
 test_dbus=yes
 test_fontconfig=yes
 test_cairo=no
+test_gdb_index=no
 
 # Default values, as such probably valid just for Linux, set
 # differently below just for Mac OSX, but at least better than
@@ -605,6 +606,7 @@ linux-gnu*|k*bsd*-gnu*)
     build_gstreamer_0_10=yes
     test_kde5=yes
     test_gtk3_kde5=yes
+    test_gdb_index=yes
     if test "$enable_fuzzers" != yes; then
         test_freetype=yes
         test_fontconfig=yes
@@ -1133,9 +1135,9 @@ libo_FUZZ_ARG_ENABLE(split-debug,
          but requires tools that support it (both build tools and debuggers).]))
 
 libo_FUZZ_ARG_ENABLE(gdb-index,
-    AS_HELP_STRING([--enable-gdb-index],
-        [Creates debug information in the gdb index format, which makes gdb start faster.
-         Requires the gold or lld linker.]))
+    AS_HELP_STRING([--disable-gdb-index],
+        [Disables creating debug information in the gdb index format, which makes gdb start faster.
+         The feature requires the gold or lld linker.]))
 
 libo_FUZZ_ARG_ENABLE(sal-log,
     AS_HELP_STRING([--enable-sal-log],
@@ -3180,31 +3182,6 @@ printf ("hello world\n");
 fi
 AC_SUBST(USE_LD)
 
-ENABLE_GDB_INDEX=
-if test "$enable_gdb_index" = "yes"; then
-    AC_MSG_CHECKING([whether $CC supports -ggnu-pubnames])
-    save_CFLAGS=$CFLAGS
-    CFLAGS="$CFLAGS -Werror -ggnu-pubnames"
-    AC_LINK_IFELSE([AC_LANG_PROGRAM([[]], [[ return 0; ]])],[ AC_MSG_RESULT( yes )],[ AC_MSG_ERROR( no )])
-
-    AC_MSG_CHECKING([whether $CC supports -Wl,--gdb-index])
-    ldflags_save=$LDFLAGS
-    LDFLAGS="$LDFLAGS -Wl,--gdb-index"
-    AC_LINK_IFELSE([AC_LANG_PROGRAM([
-#include <stdio.h>
-        ],[
-printf ("hello world\n");
-        ])], ENABLE_GDB_INDEX=TRUE, [])
-    if test "$ENABLE_GDB_INDEX" = "TRUE"; then
-        AC_MSG_RESULT( yes )
-    else
-        AC_MSG_ERROR( no )
-    fi
-    CFLAGS=$save_CFLAGS
-    LDFLAGS=$ldflags_save
-fi
-AC_SUBST(ENABLE_GDB_INDEX)
-
 HAVE_LD_BSYMBOLIC_FUNCTIONS=
 if test "$GCC" = "yes"; then
     AC_MSG_CHECKING([for -Bsymbolic-functions linker support])
@@ -3907,6 +3884,51 @@ if test "$enable_split_debug" = yes; then
     AC_SUBST(HAVE_GCC_SPLIT_DWARF)
 fi
 
+ENABLE_GDB_INDEX=
+if test "$enable_gdb_index" != "no"; then
+    dnl Currently by default enabled only on Linux, feel free to set test_gdb_index above also for other platforms.
+    if test "$enable_gdb_index" = yes -o \( "$test_gdb_index" = "yes" -o -n "$ENABLE_DEBUG$ENABLE_DBGUTIL" \); then
+        AC_MSG_CHECKING([whether $CC supports -ggnu-pubnames])
+        save_CFLAGS=$CFLAGS
+        CFLAGS="$CFLAGS -Werror -ggnu-pubnames"
+        have_ggnu_pubnames=
+        AC_LINK_IFELSE([AC_LANG_PROGRAM([[]], [[ return 0; ]])],[have_ggnu_pubnames=TRUE],[have_ggnu_pubnames=])
+        if test "$have_ggnu_pubnames" != "TRUE"; then
+            if test "$enable_gdb_index" = "yes"; then
+                AC_MSG_ERROR( no, --enable-gdb-index not supported )
+            else
+                AC_MSG_RESULT( no )
+            fi
+        else
+            AC_MSG_RESULT( yes )
+            AC_MSG_CHECKING([whether $CC supports -Wl,--gdb-index])
+            ldflags_save=$LDFLAGS
+            LDFLAGS="$LDFLAGS -Wl,--gdb-index"
+            AC_LINK_IFELSE([AC_LANG_PROGRAM([
+#include <stdio.h>
+                ],[
+printf ("hello world\n");
+                ])], ENABLE_GDB_INDEX=TRUE, [])
+            if test "$ENABLE_GDB_INDEX" = "TRUE"; then
+                AC_MSG_RESULT( yes )
+            else
+                if test "$enable_gdb_index" = "yes"; then
+                    AC_MSG_ERROR( no )
+                else
+                    AC_MSG_RESULT( no )
+                fi
+            fi
+            LDFLAGS=$ldflags_save
+        fi
+        CFLAGS=$save_CFLAGS
+        fi
+    if test -z "$ENABLE_GDB_INDEX" -a "$test_gdb_index" = "yes" -a -n "$ENABLE_DEBUG$ENABLE_DBGUTIL"; then
+        AC_MSG_WARN([Linker is not capable of creating gdb index, debugger startup will be slow.])
+        add_warning "Linker is not capable of creating gdb index, debugger startup will be slow."
+    fi
+fi
+AC_SUBST(ENABLE_GDB_INDEX)
+
 if test "$enable_sal_log" = yes; then
     ENABLE_SAL_LOG=TRUE
 fi