compiler.libraries.ldflags= was missing, generating an error when trying to link precompiled libraries

[marcel-licence]

This line is required to be compatible with the Arduino library specification

[mcspr]

Should this also be added to the combine pattern here? I have noticed esp32 platform.txt using this property
https://github.com/espressif/arduino-esp32/blob/399f4ecbb3a4cef21e2bffa37adb6190356dfb76/platform.txt#L151

Arduino/platform.txt

Line 122 in d5444c4

recipe.c.combine.pattern="{compiler.path}{compiler.c.elf.cmd}" {build.exception_flags} -Wl,-Map "-Wl,{build.path}/{build.project_name}.map" {compiler.c.elf.flags} {compiler.c.elf.extra_flags} -o "{build.path}/{build.project_name}.elf" -Wl,--start-group {object_files} "{archive_file_path}" {compiler.c.elf.libs} -Wl,--end-group "-L{build.path}"

[mcspr]

Also, some references
https://arduino.github.io/arduino-cli/0.20/platform-specification/#recipes-for-linking

Turns out this was reported to the Arduino repo last year
arduino/Arduino#10473
arduino/arduino-cli#840

[marcel-licence]

I compiled with and without the requested change and couldn't spot a difference. I am not so familar with arduino to understand what this line should do.
If you like I can just add this to the push request but it was not required to link the library.

[mcspr]

I compiled with and without the requested change and couldn't spot a difference. I am not so familar with arduino to understand what this line should do.
If you like I can just add this to the push request but it was not required to link the library.

Please do. We should also fix the comment to reference the reason why we need this?

---

tldr; this function of the arduino-cli builder uses the combine pattern:
https://github.com/arduino/arduino-cli/blob/e31a717ebc34fff80892dbbe25a9d4581906e13a/legacy/builder/phases/linker.go#L66-L123

grabbing https://github.com/BoschSensortec/BSEC-Arduino-library to reproduce this, it does not build without adding {compiler.libraries.ldflags} to the pattern group

[marcel-licence]

Okay, I've added this to the pattern group