package/poco: needs C++17

poco needs C++17 and gcc >=8 since bump to version 1.13.2 in commit
433c4fd38b15efcf74b410e5068e2e51eeba6e46 and
https://github.com/pocoproject/poco/commit/78234857bf416b718455496800d1b7be3a0d0a53
https://github.com/pocoproject/poco/commit/10f41c06d9416a6ae0884c4827ea2a91bf5d2cf8
resulting in the following build failure with gcc 7:

In file included from src/Thread.cpp:28:0:
src/Thread_POSIX.cpp: In member function 'void Poco::ThreadImpl::setNameImpl(const string&)':
src/Thread_POSIX.cpp:162:56: error: no matching function for call to 'std::__cxx11::basic_string<char>::append(const string&, std::__cxx11::basic_string<char>::size_type)'
   truncName.append(threadName, threadName.size() - half);
                                                        ^

Fixes: 433c4fd38b15efcf74b410e5068e2e51eeba6e46
 - http://autobuild.buildroot.org/results/7b1c144f39a8be4ce8f964aa13a52d0bf62dd0aa

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle <arnout@mind.be>
(cherry picked from commit 54dbd8e2c5c0b2f40cb53066b265535266eaf8d6)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/poco/Config.in

@@ -12,7 +12,7 @@ config BR2_PACKAGE_POCO
 	bool "poco"
 	depends on BR2_INSTALL_LIBSTDCPP
 	depends on BR2_USE_WCHAR
-	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_5 # C++14
+	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_8 # C++17
 	# pthread_condattr_setclock
 	depends on BR2_TOOLCHAIN_HAS_THREADS_NPTL
 	depends on !BR2_STATIC_LIBS # dlopen()
@@ -116,8 +116,8 @@ config BR2_PACKAGE_POCO_ZIP
 
 endif # BR2_PACKAGE_POCO
 
-comment "poco needs a toolchain w/ wchar, NPTL, C++, dynamic library, gcc >= 5 w/ C++14"
+comment "poco needs a toolchain w/ wchar, NPTL, C++, dynamic library, gcc >= 8"
 	depends on !BR2_USE_WCHAR || !BR2_INSTALL_LIBSTDCPP \
 		|| !BR2_TOOLCHAIN_HAS_THREADS_NPTL || BR2_STATIC_LIBS \
-		|| !BR2_TOOLCHAIN_GCC_AT_LEAST_5
+		|| !BR2_TOOLCHAIN_GCC_AT_LEAST_8
 	depends on BR2_PACKAGE_POCO_ARCH_SUPPORTS

package/poco/poco.mk

@@ -68,7 +68,6 @@ define POCO_CONFIGURE_CMDS
 	(cd $(@D); $(TARGET_MAKE_ENV) ./configure \
 		--config=Linux \
 		--prefix=/usr \
-		--cflags=-std=c++14 \
 		--ldflags="$(POCO_LDFLAGS)" \
 		--omit="$(POCO_OMIT)" \
 		$(POCO_CONF_OPTS) \