FAILED: obj/third_party/webrtc/common_audio/common_audio_c_arm_asm/filter_ar_fast_q12_armv7.o /usr/bin/cc -B/usr/local/bin -MMD -MF obj/third_party/webrtc/common_audio/common_audio_c_arm_asm/filter_ar_fast_q12_armv7.o.d -DV8_DEPRECATION_WARNINGS -DUSE_AURA=1 -DUSE_NSS_CERTS=1 -DUSE_OZONE=1 -DNO_TCMALLOC -DFULL_SAFE_BROWSING -DSAFE_BROWSING_CSD -DSAFE_BROWSING_DB_LOCAL -DCHROMIUM_BUILD -DFIELDTRIAL_TESTING_ENABLED -DTOOLKIT_QT -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -DNDEBUG -DNVALGRIND -DDYNAMIC_ANNOTATIONS_ENABLED=0 -DWEBRTC_ENABLE_PROTOBUF=1 -DHAVE_SCTP -DENABLE_EXTERNAL_AUTH -DUSE_BUILTIN_SW_CODECS -DHAVE_WEBRTC_VIDEO -DHAVE_WEBRTC_VOICE -DLOGGING_INSIDE_WEBRTC -DWEBRTC_ARCH_ARM -DWEBRTC_ARCH_ARM_V7 -DWEBRTC_NON_STATIC_TRACE_EVENT_HANDLERS=0 -DGTEST_RELATIVE_PATH -DWEBRTC_CHROMIUM_BUILD -DWEBRTC_POSIX -DWEBRTC_LINUX -DWEBRTC_BSD -DABSL_ALLOCATOR_NOTHROW=1 -Igen -I../../../../qtwebengine-everywhere-src-5.12.2/src/3rdparty/chromium -I../../../../qtwebengine-everywhere-src-5.12.2/src/3rdparty/chromium/third_party/webrtc_overrides -I../../../../qtwebengine-everywhere-src-5.12.2/src/3rdparty/chromium/third_party/webrtc -fno-strict-aliasing --param=ssp-buffer-size=4 -fstack-protector -Wno-builtin-macro-redefined -D__DATE__= -D__TIME__= -D__TIMESTAMP__= -Wno-unknown-attributes -Wno-unknown-pragmas -Wno-unknown-warning-option -funwind-tables -fPIC -pthread -fcolor-diagnostics -fmerge-all-constants -no-canonical-prefixes -std=gnu11 -mtune=generic-armv7-a -mfpu=vfpv3-d16 -g0 -c ../../../../qtwebengine-everywhere-src-5.12.2/src/3rdparty/chromium/third_party/webrtc/common_audio/signal_processing/filter_ar_fast_q12_armv7.S -o obj/third_party/webrtc/common_audio/common_audio_c_arm_asm/filter_ar_fast_q12_armv7.o ../../../../qtwebengine-everywhere-src-5.12.2/src/3rdparty/chromium/third_party/webrtc/common_audio/signal_processing/filter_ar_fast_q12_armv7.S:88:3: error: invalid instruction, any one of the following would fix this: sbfx r11, r6, #12, #16 ^ ../../../../qtwebengine-everywhere-src-5.12.2/src/3rdparty/chromium/third_party/webrtc/common_audio/signal_processing/filter_ar_fast_q12_armv7.S:88:3: note: instruction requires: armv6t2 sbfx r11, r6, #12, #16 ^ ../../../../qtwebengine-everywhere-src-5.12.2/src/3rdparty/chromium/third_party/webrtc/common_audio/signal_processing/filter_ar_fast_q12_armv7.S:88:3: note: instruction requires: thumb2 sbfx r11, r6, #12, #16 ^ ../../../../qtwebengine-everywhere-src-5.12.2/src/3rdparty/chromium/third_party/webrtc/common_audio/signal_processing/filter_ar_fast_q12_armv7.S:99:3: error: invalid instruction, any one of the following would fix this: sbfx r11, r6, #12, #16 ^ ../../../../qtwebengine-everywhere-src-5.12.2/src/3rdparty/chromium/third_party/webrtc/common_audio/signal_processing/filter_ar_fast_q12_armv7.S:99:3: note: instruction requires: armv6t2 sbfx r11, r6, #12, #16 ^ ../../../../qtwebengine-everywhere-src-5.12.2/src/3rdparty/chromium/third_party/webrtc/common_audio/signal_processing/filter_ar_fast_q12_armv7.S:99:3: note: instruction requires: thumb2 sbfx r11, r6, #12, #16 ^ ../../../../qtwebengine-everywhere-src-5.12.2/src/3rdparty/chromium/third_party/webrtc/common_audio/signal_processing/filter_ar_fast_q12_armv7.S:142:3: error: invalid instruction, any one of the following would fix this: sbfx r8, r6, #12, #16 ^ ../../../../qtwebengine-everywhere-src-5.12.2/src/3rdparty/chromium/third_party/webrtc/common_audio/signal_processing/filter_ar_fast_q12_armv7.S:142:3: note: instruction requires: armv6t2 sbfx r8, r6, #12, #16 ^ ../../../../qtwebengine-everywhere-src-5.12.2/src/3rdparty/chromium/third_party/webrtc/common_audio/signal_processing/filter_ar_fast_q12_armv7.S:142:3: note: instruction requires: thumb2 sbfx r8, r6, #12, #16 ^ https://people.freebsd.org/~jbeich/logs/112armv6/qt5-webengine-5.12.2_1.log https://people.freebsd.org/~jbeich/logs/120armv6/qt5-webengine-5.12.2_1.log https://people.freebsd.org/~jbeich/logs/head-armv6/qt5-webengine-5.12.2_1.log
I suppose it's expected that compiling a file called '...armv7.S' would fail on armv6. I suppose it's not detecting armv6 properly here, but I'm a bit out of my depth in trying to get this to build at all locally.
Closing this (reluctantly) as "that's not something we (kde@) can meaningfully support".