Turn off PGO unprofiled warning on Linux (dotnet#17262)

This warning will break the build when new files are added to the build that do not have PGO data, meaning that release builds will be broken until a new PGO collection can be run. We should not break the build if there are not counts for new files.

pgosupport.cmake

@@ -36,7 +36,7 @@ function(add_pgo TargetName)
                 if(UPPERCASE_CMAKE_BUILD_TYPE STREQUAL RELEASE OR UPPERCASE_CMAKE_BUILD_TYPE STREQUAL RELWITHDEBINFO)
                     if(NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 3.6)
                         if(HAVE_LTO)
-                            target_compile_options(${TargetName} PRIVATE -flto -fprofile-instr-use=${ProfilePath} -Wno-profile-instr-out-of-date)
+                            target_compile_options(${TargetName} PRIVATE -flto -fprofile-instr-use=${ProfilePath} -Wno-profile-instr-out-of-date -Wno-profile-instr-unprofiled)
                             set_property(TARGET ${TargetName} APPEND_STRING PROPERTY LINK_FLAGS " -flto -fuse-ld=gold -fprofile-instr-use=${ProfilePath}")
                         else(HAVE_LTO)
                             message(WARNING "LTO is not supported, skipping profile guided optimizations")