Draft: Compile liblalsimulation against libpython3.X.a for manylinux wheels

Description

This MR closes lalsuite-manylinux#3 (closed) by unpacking the compressed libpython3.X.a static libraries before compiling lalsuite for the wheels. This enables the liblalsimulation.so build to link against libpython3 (statically) to support the embedded Python waveform generator.

This properly fixes #722.

API Changes and Justification

Backwards Compatible Changes

• This change does not modify any class/function/struct/type definitions in a public C header file or any Python class/function definitions
• This change adds new classes/functions/structs/types to a public C header file or Python module

Backwards Incompatible Changes

• This change modifies an existing class/function/struct/type definition in a public C header file or Python module
• This change removes an existing class/function/struct/type from a public C header file or Python module

If any of the Backwards Incompatible check boxes are ticked please provide a justification why this change is necessary and why it needs to be done in a backwards incompatible way.

Review Status

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.gitlab-ci.yml

@@ -1160,7 +1160,15 @@ lalapps:conda:
   extends:
     - .wheel
   script:
-    - export PYTHON="/opt/python/$(echo ${CI_JOB_NAME} | sed 's/.*:\(.*\)-manylinux.*/\1/')/bin/python"
+    # get python tag from job name
+    - export PYTHON_ABI_TAG="$(echo ${CI_JOB_NAME} | sed 's/.*:\(.*\)-manylinux.*/\1/')"
+    # get prefix of manylinux Python and find python exe
+    - export PYTHON_PREFIX="/opt/python/${PYTHON_ABI_TAG}"
+    - export PYTHON="${PYTHON_PREFIX}/bin/python"
+    # add Python pkgconfig paths to enable discovery of python-3.X-embed
+    - export PKG_CONFIG_PATH="${PYTHON_PREFIX}/lib/pkgconfig:${PYTHON_PREFIX}/lib64/pkgconfig:${PKG_CONFIG_PATH}"
+    # unpack static python libraries (to enable linking liblalsimulation against them)
+    - (cd /opt/_internal && tar -xJf static-libs-for-embedding-only.tar.xz)
     # Build wheel
     - ./00boot
     - SSE="solar_system_ephemerides/ephemerides"