Additional error after the first one is fixed:

/var/tmp/portage/dev-db/mariadb-5.5.32-r10/work/mysql/sql/sql_partition.cc:285:47: error: cannot initialize a parameter of type 'HA_CREATE_INFO *' (aka 'st_ha_create_information *') with an rvalue of type 'ulonglong' (aka 'unsigned long long')
                                              (ulonglong)0, (uint)0);
                                              ^~~~~~~~~~~~
/var/tmp/portage/dev-db/mariadb-5.5.32-r10/work/mysql/sql/partition_info.h:281:72: note: passing argument to parameter 'info' here
  bool set_up_defaults_for_partitioning(handler *file, HA_CREATE_INFO *info,
                                                                       ^

Still more errors after the above two are fixed, this time due to [-Wc++11-narrowing]:

/var/tmp/portage/dev-db/mariadb-5.5.32-r10/work/mysql/sql/sql_trigger.cc:195:5: error: non-constant-expression cannot be narrowed from type 'size_t' (aka 'unsigned long') to 'int' in initializer list [-Wc++11-narrowing]
    my_offsetof(class Table_triggers_list, definitions_list),
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/tmp/portage/dev-db/mariadb-5.5.32-r10/work/mysql/include/my_global.h:869:9: note: expanded from macro 'my_offsetof'
        ((size_t)((char *)&(((TYPE *)0x10)->MEMBER) - (char*)0x10))
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/tmp/portage/dev-db/mariadb-5.5.32-r10/work/mysql/sql/sql_trigger.cc:195:5: note: insert an explicit cast to silence this issue
    my_offsetof(class Table_triggers_list, definitions_list),
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    static_cast<int>(                                       )
/var/tmp/portage/dev-db/mariadb-5.5.32-r10/work/mysql/include/my_global.h:869:9: note: expanded from macro 'my_offsetof'
        ((size_t)((char *)&(((TYPE *)0x10)->MEMBER) - (char*)0x10))
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/tmp/portage/dev-db/mariadb-5.5.32-r10/work/mysql/sql/sql_trigger.cc:200:5: error: non-constant-expression cannot be narrowed from type 'size_t' (aka 'unsigned long') to 'int' in initializer list [-Wc++11-narrowing]
    my_offsetof(class Table_triggers_list, definition_modes_list),
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...
/var/tmp/portage/dev-db/mariadb-5.5.32-r10/work/mysql/sql/sql_trigger.cc:205:5: error: non-constant-expression cannot be narrowed from type 'size_t' (aka 'unsigned long') to 'int' in initializer list [-Wc++11-narrowing]
    my_offsetof(class Table_triggers_list, definers_list),
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...
/var/tmp/portage/dev-db/mariadb-5.5.32-r10/work/mysql/sql/sql_trigger.cc:210:5: error: non-constant-expression cannot be narrowed from type 'size_t' (aka 'unsigned long') to 'int' in initializer list [-Wc++11-narrowing]
    my_offsetof(class Table_triggers_list, client_cs_names),
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...
/var/tmp/portage/dev-db/mariadb-5.5.32-r10/work/mysql/sql/sql_trigger.cc:215:5: error: non-constant-expression cannot be narrowed from type 'size_t' (aka 'unsigned long') to 'int' in initializer list [-Wc++11-narrowing]
    my_offsetof(class Table_triggers_list, connection_cl_names),
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...
/var/tmp/portage/dev-db/mariadb-5.5.32-r10/work/mysql/sql/sql_trigger.cc:220:5: error: non-constant-expression cannot be narrowed from type 'size_t' (aka 'unsigned long') to 'int' in initializer list [-Wc++11-narrowing]
    my_offsetof(class Table_triggers_list, db_cl_names),
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...
/var/tmp/portage/dev-db/mariadb-5.5.32-r10/work/mysql/sql/sql_trigger.cc:229:3: error: non-constant-expression cannot be narrowed from type 'size_t' (aka 'unsigned long') to 'int' in initializer list [-Wc++11-narrowing]
  my_offsetof(class Table_triggers_list, definition_modes_list),
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/740f240bcf1afca148978cb4b2294d3d48e7e6d5

commit 740f240bcf1afca148978cb4b2294d3d48e7e6d5
Author: Rahul Chaudhry <rahulchaudhry@chromium.org>
Date: Thu Jan 25 04:24:44 2018

dev-db/mariadb: fix build issue with llvm-next.

BUG= chromium:805000 
TEST='sudo emerge dev-db/mariadb' works with llvm-next.

Change-Id: I987176504f258e4838fc45a02263f8e6763273db
Reviewed-on: https://chromium-review.googlesource.com/882007
Commit-Ready: Rahul Chaudhry <rahulchaudhry@chromium.org>
Tested-by: Rahul Chaudhry <rahulchaudhry@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>

[add] https://crrev.com/740f240bcf1afca148978cb4b2294d3d48e7e6d5/dev-db/mariadb/files/mariadb-5.5.32-mysql-narrowing.patch
[add] https://crrev.com/740f240bcf1afca148978cb4b2294d3d48e7e6d5/dev-db/mariadb/files/mariadb-5.5.32-mysql-type-mismatch.patch
[rename] https://crrev.com/740f240bcf1afca148978cb4b2294d3d48e7e6d5/dev-db/mariadb/mariadb-5.5.32-r10.ebuild
[modify] https://crrev.com/740f240bcf1afca148978cb4b2294d3d48e7e6d5/dev-db/mariadb/mariadb-5.5.32.ebuild