icu: fix cross-build

When crossing to certain platforms, particularly when target
platform is binary compatible with host (e.g. X to X-musl).
we need to reset the LDFLAGS as otherwise -Lcross-toolchain/usr/lib
would leak into the host build and cause incorrect linkage,
preventing configuration or build.

srcpkgs/icu/template

@@ -35,7 +35,7 @@ pre_configure() {
 		cd host-build
 		env CC=cc LD=ld CXX=g++ AR=ar RANLIB=ranlib \
 			AS=as STRIP=strip CFLAGS="-Os -fPIE" CXXFLAGS="-Os -fPIE" \
-			../configure --prefix=/
+			LDFLAGS="" ../configure --prefix=/
 		make ${makejobs}
 		mkdir -p ${wrksrc}/host-icu/config
 		cp config/icucross.* ${wrksrc}/host-icu/config