app-forensics/aflplusplus: fix man page

Closes: https://bugs.gentoo.org/940252
Thanks-to: Nick Bowler <nbowler@draconx.ca>
Signed-off-by: Sam James <sam@gentoo.org>

app-forensics/aflplusplus/aflplusplus-4.08c-r1.ebuild

@@ -67,7 +67,17 @@ pkg_setup() {
 }
 
 mymake() {
-	emake \
+	# afl-fuzz spews garbage to stdout if the environment contains any
+	# variables whose name beginning with USE_ (including the underscore),
+	# regardless of their value (even if empty!).  The ebuild environment
+	# contains several such variables and the garbage that gets printed
+	# ends up in the generated man page.
+	#
+	# We can work around the problem by unsetting all these variables when
+	# running make.
+	local badvars=("${!USE_@}")
+
+	env "${badvars[@]/#/-u}" emake \
 		CC="$(tc-getCC)" \
 		CXX="$(tc-getCXX)" \
 		CFLAGS_FLTO="" \