php7: fix build of php7-mod-intl

This fixes the following build error (shortened paths for readability):

-snip-
In file included from .../php-7.1.4/ext/intl/intl_convertcpp.h:26:0,
                 from .../php-7.1.4/ext/intl/intl_convertcpp.cpp:21:
.../staging_dir/target-arm_arm926ej-s_musl_eabi/usr/include/unicode/unistr.h:56:16: error: 'UChar' does not name a type
 u_strlen(const UChar *s);
                ^
.../staging_dir/target-arm_arm926ej-s_musl_eabi/usr/include/unicode/unistr.h:80:19: error: 'char16_t' has not been declared
                   char16_t *dest, int32_t destCapacity,
                   ^
.../staging_dir/target-arm_arm926ej-s_musl_eabi/usr/include/unicode/unistr.h:81:25: error: 'char16_t' does not name a type
                   const char16_t *src, int32_t srcLength,
                         ^
In file included from .../php-7.1.4/ext/intl/intl_convertcpp.h:26:0,
                 from .../php-7.1.4/ext/intl/intl_convertcpp.cpp:21:
.../staging_dir/target-arm_arm926ej-s_musl_eabi/usr/include/unicode/unistr.h:462:16: error: 'char16_t' does not name a type
          const char16_t *srcChars) const;
                ^
[...]
-snap-

This build error was introduced by update of icu to 59.1.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>

lang/php7/Makefile

@@ -7,7 +7,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=php
 PKG_VERSION:=7.1.4
-PKG_RELEASE:=3
+PKG_RELEASE:=4
 
 PKG_MAINTAINER:=Michael Heimpold <mhei@heimpold.de>
 
@@ -245,6 +245,7 @@ endif
 
 ifneq ($(SDK)$(CONFIG_PACKAGE_php7-mod-intl),)
   CONFIGURE_ARGS+= --enable-intl=shared
+  TARGET_CPPFLAGS+= -std=c++0x
 else
   CONFIGURE_ARGS+= --disable-intl
 endif