GHA: add Linux and macOS mbedTLS jobs, fix issue

GHA: add Linux and macOS mbedTLS jobs, fix issue

- update mbedTLS repo URL.
- switch local mbedTLS build to use CMake, and Ninja.
  CMake build is required to create and install mbedTLS `pkg-config`
  files. (as of v3.6.1)
  `-DCMAKE_POSITION_INDEPENDENT_CODE=ON` required to avoid this error
  when linking mbedtls to `libcurl.so`:
  ```
  /usr/bin/ld: /home/runner/mbedtls/lib/libmbedcrypto.a(cipher.c.o): warning: relocation against `mbedtls_cipher_base_lookup_table' in read-only section `.text'
  /usr/bin/ld: /home/runner/mbedtls/lib/libmbedtls.a(ssl_tls.c.o): relocation R_X86_64_PC32 against symbol `mbedtls_x509_crt_profile_suiteb' can not be used when making a shared object; recompile with -fPIC
  /usr/bin/ld: final link failed: bad value
  ```
  Ref: https://github.com/curl/curl/actions/runs/11245069259/job/31264386723#step:40:43
- make local mbedTLS build 10x smaller by omitting programs and tests.
- GHA/linux: fix cmake warning by adding `-B .` option.
- GHA/linux: add build-only cmake job for packaged mbedTLS (2.x).
- fix compiler warning when building with mbedTLS 2.x:
  ```
  /home/runner/work/curl/curl/lib/vtls/mbedtls.c:344:1: error: ‘mbed_cipher_suite_get_str’ defined but not used [-Werror=unused-function]
    344 | mbed_cipher_suite_get_str(uint16_t id, char *buf, size_t buf_size,
        | ^~~~~~~~~~~~~~~~~~~~~~~~~
  ```
  Ref: https://github.com/curl/curl/actions/runs/11244999065/job/31264168295#step:40:50

Also in preparation for #15193
Closes #15208