cc/gcc: build lto-plugin if binutils' gold is built

To properly enable LTO with gold, gcc has to install a plugin that gold
uses to handle the LTO information.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

scripts/build/cc/gcc.sh

@@ -481,6 +481,16 @@ do_cc() {
         "") extra_config+=("--without-long-double-128");;
     esac
 
+    # If LTO is selected and binutils has gold, then enable
+    # building the lto plugin with the --enable-gold option,
+    # but only if gold has support for plugins.
+    if [    "${CT_BINUTILS_GOLD_INSTALLED}" = "y"   \
+         -a "${CT_BINUTILS_GOLD_PLUGINS}" = "y"     \
+         -a "${CT_CC_GCC_USE_LTO}" = "y"            \
+       ]; then
+        extra_config+=( --enable-gold )
+    fi
+
     CT_DoLog DEBUG "Extra config passed: '${extra_config[*]}'"
 
     # --enable-symvers=gnu really only needed for sh4 to work around a