Fix the pkgconfig file (issue #770)

Author: bcoconni

.github/workflows/cpp-python-build.yml

@@ -78,7 +78,7 @@ jobs:
       - name: Configure JSBSim
         run: |
           mkdir build && cd build
-          cmake -DCPACK_GENERATOR=DEB -DINSTALL_JSBSIM_PYTHON_MODULE=ON -DCMAKE_C_FLAGS_DEBUG="-g -O2" -DCMAKE_CXX_FLAGS_DEBUG="-g -O2" -DCMAKE_BUILD_TYPE=Debug -DSYSTEM_EXPAT=${{matrix.expat}} -DBUILD_SHARED_LIBS=${{matrix.shared_libs}} -DBUILD_JULIA_PACKAGE=${{matrix.build_julia}} -DFPECTL_DISPLAY_STACK_TRACE=${{matrix.display_stack_trace}} -DCMAKE_PREFIX_PATH=$JSBSIM_PREFIX_PATH ..
+          cmake -DCPACK_GENERATOR=DEB -DINSTALL_JSBSIM_PYTHON_MODULE=ON -DCMAKE_C_FLAGS_DEBUG="-g -O2" -DCMAKE_CXX_FLAGS_DEBUG="-g -O2" -DCMAKE_BUILD_TYPE=Debug -DSYSTEM_EXPAT=${{matrix.expat}} -DBUILD_SHARED_LIBS=${{matrix.shared_libs}} -DBUILD_JULIA_PACKAGE=${{matrix.build_julia}} -DFPECTL_DISPLAY_STACK_TRACE=${{matrix.display_stack_trace}} -DCMAKE_PREFIX_PATH=$JSBSIM_PREFIX_PATH -DCMAKE_INSTALL_PREFIX=/usr ..
       - name: Cache CTest cost data
         # This file is used by CTest to optimize the distribution of the tests
         # between the cores and reduce execution time.