fluidsynth: workaround for linking multiple definitions

Multiple defintiions for some symbols such as PC are introduced
by readline and termcap. This causes GCC 10 linking error.

Related to:
    Default to -fno-common
    https://gcc.gnu.org/gcc-10/porting_to.html

src/fluidsynth.mk

@@ -26,6 +26,7 @@ define $(PKG)_BUILD
     # compile test
     '$(TARGET)-gcc' \
         -W -Wall -Werror -ansi -pedantic \
+        -Wl,--allow-multiple-definition \
         '$(TEST_FILE)' -o '$(PREFIX)/$(TARGET)/bin/test-fluidsynth.exe' \
         `'$(TARGET)-pkg-config' --cflags --libs fluidsynth`
 endef