[HACKERS] extension build issue with PostgreSQL 10 on Centos6

There is new, not well solved dependency. I have not any problem to build extension with PostgreSQL 9.6 there

[oracle@ora2pg plpgsql_check]$ make
gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic -DLINUX_OOM_SCORE_ADJ=0 -fPIC -I/usr/pgsql-10/lib/pgxs/src/makefiles/../../src/pl/plpgsql/src -I. -I./ -I/usr/pgsql-10/include/server -I/usr/pgsql-10/include/internal -I/usr/include -D_GNU_SOURCE -I/usr/include/libxml2  -I/usr/include  -c -o plpgsql_check.oplpgsql_check.c
In file included from /usr/pgsql-10/include/server/tsearch/ts_locale.h:18,
                 from plpgsql_check.c:88:
/usr/pgsql-10/include/server/utils/pg_locale.h:19:26: error: unicode/ucol.h: Adresář nebo soubor neexistuje
In file included from /usr/pgsql-10/include/server/tsearch/ts_locale.h:18,
                 from plpgsql_check.c:88:
/usr/pgsql-10/include/server/utils/pg_locale.h:94: error: expected specifier-qualifier-list before ‘UCollator’
/usr/pgsql-10/include/server/utils/pg_locale.h:108: error: expected ‘)’ before ‘*’ token
/usr/pgsql-10/include/server/utils/pg_locale.h:109: warning: type defaults to ‘int’ in declaration of ‘UChar’
/usr/pgsql-10/include/server/utils/pg_locale.h:109: error: expected ‘;’, ‘,’ or ‘)’ before ‘*’ token
make: *** [plpgsql_check.o] Error 1

This mean not optional dependency on ICU.