toolchain.eclass: add IUSE=systemtap to gcc-8

Avoid automagic dependency on systemtap installed.

Reported-by: lekto@o2.pl
Bug: https://bugs.gentoo.org/654748
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

eclass/toolchain.eclass

@@ -154,6 +154,8 @@ if [[ ${PN} != "kgcc64" && ${PN} != gcc-* ]] ; then
 	tc_version_is_at_least 4.9 && IUSE+=" +vtv"
 	tc_version_is_at_least 5.0 && IUSE+=" jit mpx"
 	tc_version_is_at_least 6.0 && IUSE+=" +pie +ssp +pch"
+	# systemtap is a gentoo-specific switch: bug #654748
+	tc_version_is_at_least 8.0 && IUSE+=" systemtap"
 fi
 
 IUSE+=" ${IUSE_DEF[*]/#/+}"
@@ -220,6 +222,11 @@ if in_iuse gcj ; then
 	DEPEND+=" gcj? ( awt? ( ${GCJ_GTK_DEPS} ) ${GCJ_DEPS} )"
 fi
 
+if in_iuse systemtap ; then
+	# gcc needs sys/sdt.h headers on target
+	DEPEND+=" systemtap? ( dev-util/systemtap )"
+fi
+
 PDEPEND=">=sys-devel/gcc-config-1.7"
 
 #---->> S + SRC_URI essentials <<----
@@ -1229,6 +1236,10 @@ toolchain_src_configure() {
 		confgcc+=( $(use_enable mpx libmpx) )
 	fi
 
+	if in_iuse systemtap ; then
+		confgcc+=( $(use_enable systemtap) )
+	fi
+
 	if in_iuse vtv ; then
 		confgcc+=(
 			$(use_enable vtv vtable-verify)

sys-devel/gcc/metadata.xml

@@ -31,6 +31,7 @@
     <flag name="regression-test">Run the testsuite and install the results (requires FEATURES=test)</flag>
     <flag name="sanitize">Build support for various sanitizer functions (ASAN/TSAN/etc...)</flag>
     <flag name="ssp">Build packages with stack smashing protector on by default</flag>
+    <flag name="systemtap">enable systemtap static probe points</flag>
     <flag name="vtv">Build support for virtual table verification (a C++ hardening feature)</flag>
   </use>
   <upstream>