Qt OpcUA fails to build against latest Qt5.git in '5.12'

From build log:

/install/mkspecs/linux-g++ ../../src/3rdparty/open62541/open62541.c -o .obj/open62541.o
agent:2019/08/19 08:50:35 build.go:215: ../../src/3rdparty/open62541/open62541.c: In function ‘UA_findDataType’:
agent:2019/08/19 08:50:35 build.go:215: ../../src/3rdparty/open62541/open62541.c:5663:5: error: ‘for’ loop initial declarations are only allowed in C99 mode
agent:2019/08/19 08:50:35 build.go:215: for(size_t i = 0; i < UA_TYPES_COUNT; ++i) {
agent:2019/08/19 08:50:35 build.go:215: ^
agent:2019/08/19 08:50:35 build.go:215: ../../src/3rdparty/open62541/open62541.c:5663:5: note: use option -std=c99 or -std=gnu99 to compile your code
agent:2019/08/19 08:50:35 build.go:215: ../../src/3rdparty/open62541/open62541.c: In function ‘printNumber’:
agent:2019/08/19 08:50:35 build.go:215: ../../src/3rdparty/open62541/open62541.c:5776:5: error: ‘for’ loop initial declarations are only allowed in C99 mode
agent:2019/08/19 08:50:35 build.go:215: for(size_t i = digits; i > 0; --i) {
agent:2019/08/19 08:50:35 build.go:215: ^
agent:2019/08/19 08:50:35 build.go:215: ../../src/3rdparty/open62541/open62541.c: In function ‘fnv32’:
agent:2019/08/19 08:50:35 build.go:215: ../../src/3rdparty/open62541/open62541.c:5944:5: error: ‘for’ loop initial declarations are only allowed in C99 mode
agent:2019/08/19 08:50:35 build.go:215: for(size_t i = 0; i < size; ++i) {
agent:2019/08/19 08:50:35 build.go:215: ^
agent:2019/08/19 08:50:35 build.go:215: ../../src/3rdparty/open62541/open62541.c: In function ‘computeStrides’:
agent:2019/08/19 08:50:35 build.go:215: ../../src/3rdparty/open62541/open62541.c:6137:9: error: ‘for’ loop initial declarations are only allowed in C99 mode
agent:2019/08/19 08:50:35 build.go:215: for(size_t i = 0; i < dims_count; ++i)

Issue seems to be in recently added Linux SLES_12 (gcc-x86_64)