musl: Make only shared libraries conditional

External toolchain use requires a static libc (as buildroot uses
`gcc --print-file-name libc.a` to find the sysroot); thus, the static portion
of a musl build should not be conditional.

Signed-off-by: Charles Duffy <chaduffy@cisco.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/musl/musl.mk

@@ -29,7 +29,8 @@ define MUSL_CONFIGURE_CMDS
 			--prefix=/usr \
 			--libdir=/lib \
 			--disable-gcc-wrapper \
-			$(SHARED_STATIC_LIBS_OPTS))
+			--enable-static \
+			$(if $(BR2_STATIC_LIBS),--disable-shared,--enable-shared))
 endef
 
 define MUSL_BUILD_CMDS