build: RHEL8 Python Backend (triton-inference-server#385)

* PYBE RHEL

Author: fpetrini15

CMakeLists.txt

@@ -92,6 +92,18 @@ FetchContent_Declare(
   GIT_TAG "aa304c9c7d725ffb9d10af08a3b34cb372307020"
   GIT_SHALLOW ON
 )
+
+# RHEL base container has multiple version of Python installed. By default
+# it seems like pybind will pickup v3.6, so we specifically assign it to
+# search for 3.12 here.
+set(RHEL_BUILD OFF)
+if(LINUX)
+  file(STRINGS "/etc/os-release" DISTRO_ID_LIKE REGEX "ID_LIKE")
+  if(${DISTRO_ID_LIKE} MATCHES "rhel|centos")
+    set(RHEL_BUILD ON)
+    set(PYBIND11_PYTHON_VERSION 3.12)
+  endif(${DISTRO_ID_LIKE} MATCHES "rhel|centos")
+endif(LINUX)
 FetchContent_MakeAvailable(pybind11)
 
 #
@@ -268,6 +280,23 @@ target_compile_options(
 )
 target_compile_definitions(triton-python-backend-stub PRIVATE TRITON_PB_STUB)
 
+# RHEL assets are not released in a container environment nor do the current
+# Python lib versions in the manylinux base container match those currently
+# available for RHEL8 package managers. Therefore, we package the correct
+# python libs in the backend folder and adjust the stub executable to look
+# in its own folder at runtime.
+if(RHEL_BUILD)
+  set_target_properties(
+    triton-python-backend-stub
+    PROPERTIES
+      SKIP_BUILD_RPATH TRUE
+      BUILD_WITH_INSTALL_RPATH TRUE
+      INSTALL_RPATH_USE_LINK_PATH FALSE
+      INSTALL_RPATH "$\{ORIGIN\}"
+  )
+endif(RHEL_BUILD)
+
+
 # For WIN32 do not link Threads and DL_LIBS
 if(WIN32)
   target_link_libraries(