package/boost: cleanup HOST_BOOST_FLAGS

- fix alphabetical ordering
- put one module per line
- add comment explaining why options are enabled

Signed-off-by: Michael Nosthoff <buildroot@heine.tech>
Signed-off-by: Arnout Vandecappelle <arnout@mind.be>

package/boost/boost.mk

@@ -13,12 +13,39 @@ BOOST_LICENSE_FILES = LICENSE_1_0.txt
 BOOST_CPE_ID_VENDOR = boost
 
 # keep host variant as minimal as possible
+# regex & system are needed by host-riscv-isa-sim
 HOST_BOOST_FLAGS = --without-icu --with-toolset=gcc \
-	--without-libraries=$(subst $(space),$(comma),atomic chrono context \
-	contract container coroutine date_time exception fiber filesystem graph \
-	graph_parallel iostreams json locale log math mpi nowide program_options \
-	python random serialization stacktrace test thread timer \
-	type_erasure url wave)
+	--without-libraries=$(subst $(space),$(comma),\
+	atomic \
+	chrono container \
+	context \
+	contract \
+	coroutine \
+	date_time \
+	exception \
+	fiber \
+	filesystem \
+	graph \
+	graph_parallel \
+	iostreams \
+	json \
+	locale \
+	log \
+	math \
+	mpi \
+	nowide \
+	program_options \
+	python \
+	random \
+	serialization \
+	stacktrace \
+	test \
+	thread \
+	timer \
+	type_erasure \
+	url \
+	wave\
+	)
 
 BOOST_WITHOUT_FLAGS += $(if $(BR2_PACKAGE_BOOST_ATOMIC),,atomic)
 BOOST_WITHOUT_FLAGS += $(if $(BR2_PACKAGE_BOOST_CHRONO),,chrono)