Name fake-SAI agent binaries with -sai_impl suffix

The BUILD_SAI_FAKE arm now builds the agents with the -sai_impl suffix
(and is made mutually exclusive with the real-SAI SAI_IMPL path via
elseif), and fboss_fake_agent_targets depends on wedge_agent-sai_impl /
fboss_hw_agent-sai_impl. This lands fake-SAI builds at the
/opt/fboss/bin paths the systemd units and package.py already reference,
so the fboss-sim runtime no longer needs the -fake -> -sai_impl
symlinks.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: hillol-nexthop

CMakeLists.txt

@@ -1341,8 +1341,8 @@ add_dependencies(fboss_fake_agent_targets
   fboss_agent_thrift_libs
   fboss_sw_agent
   sai_replayer-fake
-  wedge_agent-fake
-  fboss_hw_agent-fake
+  wedge_agent-sai_impl
+  fboss_hw_agent-sai_impl
 )
 
 add_custom_target(fboss_fake_agent_test_targets)

cmake/AgentPlatformsSai.cmake

@@ -206,10 +206,11 @@ find_library(SAI_IMPL sai_impl)
 message(STATUS "SAI_IMPL: ${SAI_IMPL}")
 
 if(BUILD_SAI_FAKE)
-  BUILD_SAI_WEDGE_AGENT("fake" fake_sai)
-endif()
-
-if(SAI_IMPL)
+  # Name fake-SAI agent binaries with the -sai_impl suffix so they sit at
+  # the same /opt/fboss/bin/ paths the systemd unit files reference and
+  # package.py FORWARDING_BINARIES matches without modification.
+  BUILD_SAI_WEDGE_AGENT("sai_impl" fake_sai)
+elseif(SAI_IMPL)
   BUILD_SAI_WEDGE_AGENT("sai_impl" ${SAI_IMPL})
   install(
     TARGETS