external/icu: Work around a weird Windows bug in either make or clang-cl

...for now; workdir/UnpackedTarball/icu/source/tools/toolutil/Makefile invokes
the compiler with a -DU_HOST=\"...\" argument, and apparently directly executes
the compiler from CreateProcess, not going via a shell invocation for the recipe
line.  This confuses clang-cl for whatever reason, and for whatever other
reason, forcing make to go via a shell invocation (by adding "true &&" into the
recipe line) fixes it.

Change-Id: I3757a8856f93228c19475b37f3037fa9519a426f

external/icu/clang-cl.patch.0

@@ -1,3 +1,16 @@
+--- source/config/mh-cygwin-msvc
++++ source/config/mh-cygwin-msvc
+@@ -51,8 +51,8 @@
+ LDFLAGS+=-nologo
+ 
+ # Commands to compile
+-COMPILE.c=	$(CC) $(CPPFLAGS) $(DEFS) $(CFLAGS) -c
++COMPILE.c=	true && $(CC) $(CPPFLAGS) $(DEFS) $(CFLAGS) -c
+-COMPILE.cc=	$(CXX) $(CPPFLAGS) $(DEFS) $(CXXFLAGS) -c
++COMPILE.cc=	true && $(CXX) $(CPPFLAGS) $(DEFS) $(CXXFLAGS) -c
+ 
+ # Commands to link
+ LINK.c=		LINK.EXE -subsystem:console $(LDFLAGS)
 --- source/runConfigureICU
 +++ source/runConfigureICU
 @@ -259,8 +259,8 @@