[LG Optimus L90] clorophilla:
So, after a lot of effort (documentation on ROM building won't make it any easier), I managed to reach the last stage (the building process itself with "brunch w7") on LineageOS 14.1. But this happens: (OBS: cut some text before this part, just a bunch of text commands)

PLATFORM_VERSION_CODENAME=REL
PLATFORM_VERSION=7.1.2
LINEAGE_VERSION=14.1-20190908-UNOFFICIAL-w7
TARGET_PRODUCT=lineage_w7
TARGET_BUILD_VARIANT=userdebug
TARGET_BUILD_TYPE=release
TARGET_BUILD_APPS=
TARGET_ARCH=arm
TARGET_ARCH_VARIANT=armv7-a-neon
TARGET_CPU_VARIANT=krait
TARGET_2ND_ARCH=
TARGET_2ND_ARCH_VARIANT=
TARGET_2ND_CPU_VARIANT=
HOST_ARCH=x86_64
HOST_2ND_ARCH=x86
HOST_OS=linux
HOST_OS_EXTRA=Linux-5.0.0-27-generic-x86_64-with-LinuxMint-19.2-tina
HOST_CROSS_OS=windows
HOST_CROSS_ARCH=x86
HOST_CROSS_2ND_ARCH=x86_64
HOST_BUILD_TYPE=release
BUILD_ID=NJH47F
OUT_DIR=/home/android/android/lineage14/out
============================================
Checking build tools versions...
frameworks/av/camera/cameraserver/Android.mk:18: Target has integrated cameraserver into mediaserver. This is weakening security measures introduced in 7.0
find: ‘/home/android/android/lineage14/out/target/common/obj/SHARED_LIBRARIES/libwifi-hal-mock_intermediates’: Arquivo ou diretório inexistente
build/core/dex_preopt.mk:74: warning: overriding commands for target `/home/android/android/lineage14/out/target/product/w7/dex_bootjars/system/framework/telephony-ext_nodex.jar'
build/core/dex_preopt.mk:74: warning: ignoring old commands for target `/home/android/android/lineage14/out/target/product/w7/dex_bootjars/system/framework/telephony-ext_nodex.jar'
Starting build with ninja
ninja: Entering directory `.'
[ 0% 328/34549] host Java: tagsouplib (/home/android/android/lineage14/out/host/common/obj/JAVA_LIBRARIES/tagsouplib_intermediates/classes)
Note: Some input files use unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
[ 1% 469/34549] host Java: antlr-runtime (/home/android/android/lineage14/out/host/common/obj/JAVA_LIBRARIES/antlr-runtime_intermediates/classes)
Note: Some input files use unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
[ 1% 487/34549] host Java: guavalib (/home/android/android/lineage14/out/host/common/obj/JAVA_LIBRARIES/guavalib_intermediates/classes)
warning: [options] bootstrap class path not set in conjunction with -source 1.7
Note: Some input files use or override a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
Note: Some input files use unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
1 warning
[ 1% 611/34549] host Java: jsilver (/home/android/android/lineage14/out/host/common/obj/JAVA_LIBRARIES/jsilver_intermediates/classes)
Note: external/jsilver/src/org/clearsilver/FactoryLoader.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
[ 1% 683/34549] host Java: doclava (/home/android/android/lineage14/out/host/common/obj/JAVA_LIBRARIES/doclava_intermediates/classes)
Note: Some input files use unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
[ 2% 693/34549] Lex: aidl <= system/tools/aidl/aidl_language_l.ll
FAILED: /bin/bash -c "prebuilts/misc/linux-x86/flex/flex-2.5.39 -o/home/android/android/lineage14/out/host/linux-x86/obj/STATIC_LIBRARIES/libaidl-common_intermediates/aidl_language_l.cpp system/tools/aidl/aidl_language_l.ll"
flex-2.5.39: loadlocale.c:130: _nl_intern_locale_data: Assertiva "cnt < (sizeof (_nl_value_type_LC_TIME) / sizeof (_nl_value_type_LC_TIME[0]))" falhou.
Aborted (core dumped)
[ 2% 693/34549] target Java: core-all (/home/android/android/lineage14/out/target/common/obj/JAVA_LIBRARIES/core-all_intermediates/classes)
Note: Some input files use or override a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
Note: Some input files use unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
ninja: build stopped: subcommand failed.
make: *** [build/core/ninja.mk:152: ninja_wrapper] Error 1
make: Leaving directory '/home/android/android/lineage14'

#### make failed to build some targets (03:36 (mm:ss)) ####

android@Android-VM:~/android/lineage14

and I don't know what to do now. Can someone help if I'm doing something wrong?