x42-plugins: Failure on current nixpkgs-unstable

gistfile1.txt

@nix { "action": "setPhase", "phase": "unpackPhase" }
unpacking sources
@nix { "action": "setPhase", "phase": "patchPhase" }
patching sources
patching script interpreter paths in ./stepseq.lv2/gridgen.sh
./stepseq.lv2/gridgen.sh: interpreter directive changed from "/bin/bash" to "/nix/store/6vqgi9d49smsbr2qxra52yhipg0yxf9f-bash-4.4-p23/bin/bash"
@nix { "action": "setPhase", "phase": "updateAutotoolsGnuConfigScriptsPhase" }
updateAutotoolsGnuConfigScriptsPhase
@nix { "action": "setPhase", "phase": "configurePhase" }
configuring
no configure script, doing nothing
@nix { "action": "setPhase", "phase": "buildPhase" }
building
build flags: SHELL=/nix/store/6vqgi9d49smsbr2qxra52yhipg0yxf9f-bash-4.4-p23/bin/bash PREFIX=\$\(out\) FONTFILE=/nix/store/y1hybm8h1kln0hg06c42m4g1wsblc0ig-freefont-ttf-20120503/share/fonts/truetype/FreeSansBold.ttf
test -d .git -a .gitmodules -a -f Makefile.git && make -f Makefile.git submodule_check
make: [Makefile:25: submodule_check] Error 1 (ignored)
make -C balance.lv2 
make[1]: Entering directory '/build/x42-plugins-20180320/balance.lv2'
Version: 0.6.6 -> 0 6 6 
LV2 Version: 1548 0
sed "s/@LV2NAME@/balance/;s/@LIB_EXT@/.so/" \
  manifest.ttl.in > build/manifest.ttl
sed "s/@LV2NAME@/balance/;s/@LV2GUI@/balanceUI/;s/@LIB_EXT@/.so/;s/@UI_TYPE@/X11UI/" \
	manifest.ui.ttl.in >> build/manifest.ttl
sed "s/@VERSION@/lv2:microVersion 0 ;lv2:minorVersion 1548 ;/g" \
	balance.ttl.in > build/balance.ttl
sed "s/@UI_TYPE@/X11UI/;s/@UI_REQ@/lv2:requiredFeature ui:idleInterface; lv2:extensionData ui:idleInterface;/;" \
	balance.ui.ttl.in >> build/balance.ttl
g++  -msse -msse2 -mfpmath=sse -ffast-math -fomit-frame-pointer -O3 -fno-finite-math-only -Wall -fPIC `pkg-config --cflags lv2` -DHAVE_LV2_1_8 \
  -o build/balance.so balance.c \
  -shared -Wl,-Bstatic -Wl,-Bdynamic  -lm
g++: error: unrecognized command line option '-msse'; did you mean '-fdse'?
g++: error: unrecognized command line option '-msse2'
g++: error: unrecognized command line option '-mfpmath=sse'
make[1]: *** [Makefile:192: build/balance.so] Error 1
make[1]: Leaving directory '/build/x42-plugins-20180320/balance.lv2'
make: *** [Makefile:17: balance.lv2] Error 2