build(bugfix):fix uClibc++ layout build error

make[2]: *** No rule to make target '/home/nuttx/libs/libxx/uClibc++/tests/testframework.cpp',
needed by '/home/nuttx/libs/libxx/uClibc++/tests/testframework.cpp.home.apps.testing.uclibcxx_test.o'.  Stop.

Signed-off-by: haopengxiang <haopengxiang@xiaomi.com>

Author: pengxianghao21

testing/uclibcxx_test/Makefile

@@ -22,7 +22,7 @@ include $(APPDIR)/Make.defs
 
 CXXEXT := .cpp
 
-TESTDIR = $(TOPDIR)/libs/libxx/uClibc++/tests
+TESTDIR = $(TOPDIR)/libs/libxx/uClibc++/uClibc++/tests
 ORIGS  := $(wildcard $(TESTDIR)/*.cpp)
 
 BLACKSRCS := wchartest.cpp