x86: # /usr/lib/qt5/bin/uic -> Illegal instruction

We have a tiny qt5 application which has compiled and run previously under v3.14 on x86 (target computer is a Vortex86 SoC). Now I have just hit an error in building, which seems to come from this:

device-001beb561648:~# /usr/lib/qt5/bin/uic
Illegal instruction

/proc/cpuinfo:

processor       : 0
vendor_id       : Vortex86 SoC
cpu family      : 5
model           : 2
model name      : 05/02
stepping        : 2
cpu MHz         : 799.972
physical id     : 0
siblings        : 1
core id         : 0
cpu cores       : 1
apicid          : 0
initial apicid  : 0
fdiv_bug        : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu tsc cx8 cpuid
bugs            : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds swapgs itlb_multihit
bogomips        : 1600.60
clflush size    : 32
cache_alignment : 32
address sizes   : 32 bits physical, 32 bits virtual
power management:

Program received signal SIGILL, Illegal instruction.
0xb7a3b747 in qCalculateBlockSize(unsigned int, unsigned int, unsigned int) () from /usr/lib/libQt5Core.so.5
#0  0xb7a3b747 in qCalculateBlockSize(unsigned int, unsigned int, unsigned int) () from /usr/lib/libQt5Core.so.5
No symbol table info available.
#1  0xb7a3b85b in QArrayData::allocate(unsigned int, unsigned int, unsigned int, QFlags<QArrayData::AllocationOption>)
    () from /usr/lib/libQt5Core.so.5
No symbol table info available.
#2  0xb7ab3639 in QString::fromLatin1_helper(char const*, int) () from /usr/lib/libQt5Core.so.5
No symbol table info available.
#3  0x0040bda5 in ?? ()
--Type <RET> for more, q to quit, c to continue without paging--
No symbol table info available.
#4  0xb7fc549f in do_init_fini (queue=<optimized out>) at ldso/dynlink.c:1539
        n = <optimized out>
        fn = 0x474170
        p = 0xb7ffea20 <app>
        dyn = {1253981294, 7727, 1592, 490500, 0, 3936, 448, 0, 0, 0, 7759, 16, 45056, 271377, 0, 0, 0, 12180, 29288,
          8, 17, 3087003856, 0, 41468, 0, 475500, 0, 4, 0, 0, 8, 0}
        i = <optimized out>
        self = 0xb74f5df8
#5  0xb7fc671b in __libc_start_init () at ldso/dynlink.c:1552
No locals.
#6  0xb7f82ee6 in libc_start_main_stage2 (main=0x40be3d, argc=1, argv=0xbffffd44) at src/env/__libc_start_main.c:91
        envp = <optimized out>
#7  0x0040bebd in ?? ()
No symbol table info available.
(gdb)