Error: assigning to 'OpenImageIO_v2_6_5::TextureSystem *' from incompatible type 'std::shared_ptr<TextureSystem>'

### Problem
**Actual behavior:**

FAILED: src/liboslexec/CMakeFiles/oslexec.dir/shadingsys.cpp.o
/usr/lib/llvm14/bin/clang++ -DCUDA_TARGET_ARCH=\"sm_60\" -DOIIO_DISABLE_DEPRECATED=900000 -DOIIO_HIDE_FORMAT=1 -DOSL_CUDA_VERSION=\"\" -DOSL_EXPORTS -DOSL_FAST_MATH=1 -DOSL_INTERNAL=1 -DOSL_LLVM_FULL_VERSION=\"14.0.6\" -DOSL_LLVM_VERSION=140 -DOSL_OPTIX_VERSION=\"\" -D__STDC_CONSTANT_MACROS -D__STDC_LIMIT_MACROS -Doslexec_EXPORTS -Doslparse=OSL_v1_14_1_oslparse -Dosoparse=OSL_v1_14_1_osoparse -I./OpenShadingLanguage/build/include -I./OpenShadingLanguage/build/src/include -I./OpenShadingLanguage/src/include -I./OpenShadingLanguage/ext/dist/include -I./OpenShadingLanguage/src/liboslexec -I./OpenShadingLanguage/src/liboslcomp -isystem /usr/lib/llvm14/include -isystem /usr/include/Imath -march=native -mtune=native -O2 -pipe -fpermissive -fno-plt -fexceptions -Wformat -Wno-deprecated-declarations -Wno-stringop-overflow -Wno-unknown-pragmas -Wno-error=incompatible-pointer-types -fPIC -Wp,-D_GLIBCXX_ASSERTIONS -Wno-template-id-cdtor -Wno-zero-as-null-pointer-constant -fPIC -D__STDC_LIMIT_MACROS -D__STDC_CONSTANT_MACROS -O3 -DNDEBUG -std=c++17 -fPIC -fvisibility=hidden -Wall -Wno-unused-function -Wno-overloaded-virtual -Wno-unneeded-internal-declaration -Wno-unused-private-field -Wno-tautological-compare -Wno-unknown-pragmas -Wno-format-security -Qunused-arguments -Wunknown-warning-option -Wno-unused-local-typedefs -Wno-expansion-to-defined -Wno-bitwise-instead-of-logical -Wno-null-conversion -Wno-error=strict-overflow -fno-math-errno -fno-reciprocal-math -MD -MT src/liboslexec/CMakeFiles/oslexec.dir/shadingsys.cpp.o -MF src/liboslexec/CMakeFiles/oslexec.dir/shadingsys.cpp.o.d -o src/liboslexec/CMakeFiles/oslexec.dir/shadingsys.cpp.o -c ./OpenShadingLanguage/src/liboslexec/shadingsys.cpp
./OpenShadingLanguage/src/liboslexec/shadingsys.cpp:1204:24: error: assigning to 'OpenImageIO_v2_6_5::TextureSystem *' from incompatible type 'std::shared_ptr'
m_texturesys = TextureSystem::create(true /* shared */);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

### Steps to Reproduce

I could overcome this error by patching https://github.com/AcademySoftwareFoundation/OpenShadingLanguage/pull/1848 in reverse.

### Versions

* OSL branch/version: git master (1.13.11.0+)
* OS: Linux
* C++ compiler: 14.2.1
* LLVM version: 14 (went back from 18)
* OIIO version: git master - shall I get behind https://github.com/OpenImageIO/oiio.git#commit=135e659301a3f767a05da1d6a3cc472d1563402d ?

Start in src/liboslexec/shadingsys.cpp around line 1204 and compare the TextureSystem::create API used there with the reported OpenImageIO version. Review the reverse of pull request 1848 and reproduce the build with the listed LLVM, compiler, and OIIO setup. Done means the project compiles without the incompatible-pointer error.

Written by the indexing model from the issue text.