tools/export: prefix each linker script in toolchain.cmake

[r3wretrhy]

tools/export: prefix each linker script in toolchain.cmake.

Summary

• Why change is necessary: make export writes several names into LDNAME, but the exported toolchain.cmake only prefixes the first file with the scripts directory.
• What functional part of the code is being changed: tools/toolchain.cmake.export linker-script path generation.
• How: split LDNAME, prefix every script with the normalized export scripts path, and pass each as its own -T argument.
• Related NuttX Issue: [BUG] ESP32S3: make export generates broken toolchain.cmake with multiple LDNAME files, then build stopped: cannot find esp32s3_rom_aliases.ld flat_memory.ld esp32s3_sections.ld #19820

Impact

• Is new feature added? Is existing feature changed? NO. Fixes exported CMake toolchain files for boards with more than one linker script.
• Impact on user (will user need to adapt to change)? NO
• Impact on build (will build process change)? YES. Out-of-tree CMake apps that consume make export now receive a -T path for every LDNAME script.
• Impact on hardware (will arch(s) / board(s) / driver(s) change)? NO
• Impact on documentation (is update required / provided)? NO
• Impact on security (any sort of implications)? NO
• Impact on compatibility (backward/forward/interoperability)? NO. Single-script LDNAME still produces one -T argument.

Testing

I confirm that changes are verified on local setup and works as intended:

• Build Host(s): Windows 11, CMake 3.29.2
• Target(s): cmake -P reconstruction of the reported ESP32-S3 LDNAME list from [BUG] ESP32S3: make export generates broken toolchain.cmake with multiple LDNAME files, then build stopped: cannot find esp32s3_rom_aliases.ld flat_memory.ld esp32s3_sections.ld #19820, plus the single-script gnu-elf.ld case

Testing logs before change:

OLD_RULE=-T/tmp/nuttx-export-13.0.0/scripts/../scripts/esp32s3_peripherals.ld esp32s3_rom_aliases.ld flat_memory.ld esp32s3_sections.ld

Testing logs after change:

NUTTX_PATH=/tmp/nuttx-export-13.0.0 NEW_RULE=-T/tmp/nuttx-export-13.0.0/scripts/esp32s3_peripherals.ld -T/tmp/nuttx-export-13.0.0/scripts/esp32s3_rom_aliases.ld -T/tmp/nuttx-export-13.0.0/scripts/flat_memory.ld -T/tmp/nuttx-export-13.0.0/scripts/esp32s3_sections.ld EXPORT_LDNAME_OK

PR verification Self-Check

• This PR introduces only one functional change.
• I have updated all required description fields above.
• My PR adheres to Contributing Guidelines and Documentation (git commit title and message, coding standard, etc).
• My PR is still work in progress (not ready for review).
• My PR is ready for review and can be safely merged into a codebase.

[github-actions]

MemBrowse Memory Report

No memory changes detected for:

• arduino-mega2560
• esp32-devkitc
• hifive1-revb
• mirtoo
• qemu-armv8a
• qemu-intel64
• rx65n-rsk2mb
• s698pm-dkit
• stm32-nucleo-f103rb