I cannot build the current master (a422b171ac17edde296b48e2b3e9c9845d773609) or tag 19.07.1 because the linker is unable to link the hostapd binary:
make[4]: Entering directory '/home/FE/kappen/sdwn/openwrt/build_dir/target-x86_64_musl/hostapd-full-internal/hostapd-2019-08-08-ca8c2bd2/hostapd'
/home/FE/kappen/sdwn/openwrt/staging_dir/toolchain-x86_64_gcc-8.3.0_musl/lib/gcc/x86_64-openwrt-linux-musl/8.3.0/../../../../x86_64-openwrt-linux-musl/bin/ld: /home/FE/kappen/sdwn/openwrt/tmp/cc3lWBkw.ltrans7.ltrans.o: in function `br_addif':
<artificial>:(.text+0x449): undefined reference to `linux_br_add_if'
/home/FE/kappen/sdwn/openwrt/staging_dir/toolchain-x86_64_gcc-8.3.0_musl/lib/gcc/x86_64-openwrt-linux-musl/8.3.0/../../../../x86_64-openwrt-linux-musl/bin/ld: /home/FE/kappen/sdwn/openwrt/tmp/cc3lWBkw.ltrans7.ltrans.o: in function `vlan_get_bridge':
<artificial>:(.text+0x868): undefined reference to `linux_br_add'
/home/FE/kappen/sdwn/openwrt/staging_dir/toolchain-x86_64_gcc-8.3.0_musl/lib/gcc/x86_64-openwrt-linux-musl/8.3.0/../../../../x86_64-openwrt-linux-musl/bin/ld: /home/FE/kappen/sdwn/openwrt/tmp/cc3lWBkw.ltrans7.ltrans.o: in function `br_delif':
<artificial>:(.text+0xa55): undefined reference to `linux_br_del_if'
/home/FE/kappen/sdwn/openwrt/staging_dir/toolchain-x86_64_gcc-8.3.0_musl/lib/gcc/x86_64-openwrt-linux-musl/8.3.0/../../../../x86_64-openwrt-linux-musl/bin/ld: /home/FE/kappen/sdwn/openwrt/tmp/cc3lWBkw.ltrans7.ltrans.o: in function `vlan_put_bridge':
<artificial>:(.text+0xd54): undefined reference to `linux_br_del'
/home/FE/kappen/sdwn/openwrt/staging_dir/toolchain-x86_64_gcc-8.3.0_musl/lib/gcc/x86_64-openwrt-linux-musl/8.3.0/../../../../x86_64-openwrt-linux-musl/bin/ld: /home/FE/kappen/sdwn/openwrt/tmp/cc3lWBkw.ltrans9.ltrans.o: in function `ap_sta_add':
<artificial>:(.text+0x6908): undefined reference to `sta_track_claim_taxonomy_info'
collect2: error: ld returned 1 exit status
I even get the sta_track_claim_taxonomy_info error on tag 18.06.7.