Wait, It may have actually worked. I see a .elf file and .bin file gets created, despite the warnings.
The errors occur after the bin file is created.
I’m assuming everything is actually working; if not, I’ll post back later, but thought leaving this post may be helpful to others.
*** [.pio/build/demo/src/EMailSender.o] Error 1
Linking .pio/build/d1_mini/firmware.elf
Retrieving maximum program size .pio/build/d1_mini/firmware.elf
Checking size .pio/build/d1_mini/firmware.elf
Advanced Memory Usage is available via "PlatformIO Home > Project Inspect"
RAM: [===== ] 49.0% (used 40116 bytes from 81920 bytes)
Flash: [===== ] 54.6% (used 569785 bytes from 1044464 bytes)
Building .pio/build/d1_mini/firmware.bin
Creating BIN file ".pio/build/d1_mini/firmware.bin" using "/home/linuxlite/.platformio/packages/framework-arduinoespressif8266/bootloaders/eboot/eboot.elf" and ".pio/build/d1_mini/firmware.elf"
===================================================== [SUCCESS] Took 89.34 seconds =====================================================
====================================================== [FAILED] Took 0.67 seconds ======================================================
Environment Status Duration
-------------------- -------- ------------
d1_mini SUCCESS 00:01:29.338
sanguino_atmega1284p SUCCESS 00:00:14.022
linux FAILED 00:00:00.946
demo FAILED 00:00:00.668
================================================= 2 failed, 2 succeeded in 00:01:44.974 =================================================