build: fix LDFLAGS overriding issue.

test/Makefile.am

@@ -61,7 +61,8 @@ meshviewer_SOURCES = meshviewer.cpp \
     shinymvtexture.lolfx shinyfur.lolfx mviewer_em_test.lolfx
 meshviewer_CPPFLAGS = $(AM_CPPFLAGS)
 meshviewer_DEPENDENCIES = @LOL_DEPS@
+meshviewer_LDFLAGS = $(AM_LDFLAGS)
 if USE_EMSCRIPTEN
-meshviewer_LDFLAGS = $(AM_LDFLAGS) -s EXPORTED_FUNCTIONS="['_main', '_C_Send']"
+meshviewer_LDFLAGS += -s EXPORTED_FUNCTIONS="['_main', '_C_Send']"
 endif