devel/php*-intl: unbreak with ICU 61

In file included from ext/intl/intl_convertcpp.cpp:21:
./intl_convertcpp.h:29:25: error: unknown type name 'UnicodeString'
int intl_stringFromChar(UnicodeString &ret, char *str, size_t str_len, UErrorCode *status);

^

./intl_convertcpp.h:31:40: error: unknown type name 'UnicodeString'; did you mean 'icu::UnicodeString'?
zend_string* intl_charFromString(const UnicodeString &from, UErrorCode *status);

^~~~~~~~~~~~~
icu::UnicodeString

/usr/local/include/unicode/unistr.h:286:20: note: 'icu::UnicodeString' declared here
class U_COMMON_API UnicodeString : public Replaceable

^

ext/intl/intl_convertcpp.cpp:28:25: error: unknown type name 'UnicodeString'
int intl_stringFromChar(UnicodeString &ret, char *str, size_t str_len, UErrorCode *status)

^

ext/intl/intl_convertcpp.cpp:59:40: error: unknown type name 'UnicodeString'; did you mean 'icu::UnicodeString'?
zend_string* intl_charFromString(const UnicodeString &from, UErrorCode *status)

^~~~~~~~~~~~~
icu::UnicodeString

/usr/local/include/unicode/unistr.h:286:20: note: 'icu::UnicodeString' declared here
class U_COMMON_API UnicodeString : public Replaceable

^

https://ssl.icu-project.org/trac/changeset/40705

PR: 227042
Reported by: antoine (via exp-run)