Precompiled libraries include path doesn't include FPU variant

[mike1808]

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---

Configuration

Operating system: Linux workstation 5.15.71-1-MANJARO

PlatformIO Version (platformio --version): PlatformIO Core, version 6.1.6a

Description of problem

Some precompiled arduino libraries have the FPU variant in the source and include the library depending on it.
For instance, Adafruit nRFCrypto library has `fpv4-sp-d16-hard

Steps to Reproduce

1. Create a new project with nrf52 platform and Arduino framework and add nRFCrypto to the depedencies:

[env:nrf52]
platform = nordicnrf52
board = adafruit_feather_nrf52840
framework = arduino
lib_deps = 
  adafruit/Adafruit nRFCrypto@^0.0.7

2. Compile

Actual Results

Fails to link:

Linking .pio/build/adafruit_feather_nrf52840/firmware.elf
/home/USER/.platformio/packages/toolchain-gccarmnoneeabi/bin/../lib/gcc/arm-none-eabi/7.2.1/../../../../arm-none-eabi/bin/ld: cannot find -lnrf_cc310_0.9.13-no-interrupts
collect2: error: ld returned 1 exit status
*** [.pio/build/xiaonrf_adafruit/firmware.elf] Error 1

Expected Results

To successfully link.

If problems with PlatformIO Build System:

The content of platformio.ini:

[env:nrf52]
platform = nordicnrf52
board = adafruit_feather_nrf52840
framework = arduino
lib_deps = 
	adafruit/Adafruit nRFCrypto@^0.0.7```

**Source file to reproduce issue:**
```cpp
Insert here...

Additional info

[maxgerhardt]

Related: #4056

Offending code:

platformio-core/platformio/builder/tools/piolib.py

Lines 607 to 617 in b11925a

	if self._manifest.get("precompiled") in ("true", "full"):
	# add to LDPATH {build.mcu} folder
	board_config = self.env.BoardConfig()
	for key in ("build.mcu", "build.cpu"):
	libpath = os.path.join(self.src_dir, board_config.get(key, ""))
	if not os.path.isdir(libpath):
	continue
	self.env.PrependUnique(LIBPATH=libpath)
	break
	ldflags = [flag for flag in ldflags if flag] # remove empty
	return " ".join(ldflags) if ldflags else None

Doesn't work with https://github.com/adafruit/Adafruit_nRFCrypto/blob/master/library.properties and src/cortex-m4/fpv4-sp-d16-hard/libnrf_cc310_0.9.13-no-interrupts.a

[maxgerhardt]

I think another user just hit this in https://community.platformio.org/t/motionfx-library-compile-failed-under-the-pio-but-success-under-arduino-ide/37975/3?u=maxgerhardt: With

[env:nucleo_f401re]
platform = ststm32
board = nucleo_f401re
framework = arduino
lib_deps = 
   stm32duino/STM32duino MotionFX @ ^1.1.0

it does not work out of the box either, it doesn't link in the the right library at all (no -lMotionFX) and from the wrong folder (just src/cortex-m4 instead of the right src/cortex-m4/fpv4-sp-d16-hard in this case).