Do not include non-standardized xlocale.h, include locale.h instead

"The file and this data structure is not standardized.  Don't rely on it.  It
can go away without warning."

...

And since glibc 2.26 it's gone.

https://ssl.icu-project.org/trac/ticket/13329

Change-Id: Iaf595b9c1be4eaab4306acb2c63c5a13dcb7a4e3
Reviewed-on: https://gerrit.libreoffice.org/42219Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Jenkins <ci@libreoffice.org>

external/icu/UnpackedTarball_icu.mk

@@ -35,6 +35,7 @@ $(eval $(call gb_UnpackedTarball_add_patches,icu,\
 	external/icu/icu4c-59-werror-undef.patch.1 \
 	external/icu/icu4c-59-werror-shadow.patch.1 \
 	external/icu/icu4c-iOS.patch.1 \
+	external/icu/icu4c-59-icu13329-xlocale.patch.1 \
 ))
 
 $(eval $(call gb_UnpackedTarball_add_file,icu,source/data/brkitr/khmerdict.dict,external/icu/khmerdict.dict))

external/icu/icu4c-59-icu13329-xlocale.patch.1

+# xlocale.h is gone with glibc 2.26 and should never had been included.
+# https://ssl.icu-project.org/trac/ticket/13329
+diff -ur icu.org/source/i18n/digitlst.cpp icu/source/i18n/digitlst.cpp
+--- icu.org/source/i18n/digitlst.cpp	2017-01-20 01:20:31.000000000 +0100
++++ icu/source/i18n/digitlst.cpp	2017-09-12 22:03:15.019034749 +0200
+@@ -64,7 +64,7 @@
+ # if U_PLATFORM_USES_ONLY_WIN32_API || U_PLATFORM == U_PF_CYGWIN
+ #   include <locale.h>
+ # else
+-#   include <xlocale.h>
++#   include <locale.h>
+ # endif
+ #endif
+