Add gcov command to gcc-15 and 16 toolchains

Author: steve-downey

etc/gcc-15-toolchain.cmake

@@ -4,6 +4,7 @@ include("${CMAKE_CURRENT_LIST_DIR}/gcc-flags.cmake")
 
 set(CMAKE_C_COMPILER gcc-15)
 set(CMAKE_CXX_COMPILER g++-15)
+set(GCOV_EXECUTABLE "gcov-15" CACHE STRING "GCOV executable" FORCE)
 
 set(CMAKE_CXX_FLAGS_ASAN
     "${CMAKE_CXX_FLAGS_ASAN} -Wno-maybe-uninitialized"

etc/gcc-16-toolchain.cmake

@@ -4,6 +4,7 @@ include("${CMAKE_CURRENT_LIST_DIR}/gcc-flags.cmake")
 
 set(CMAKE_C_COMPILER gcc-16)
 set(CMAKE_CXX_COMPILER g++-16)
+set(GCOV_EXECUTABLE "gcov-16" CACHE STRING "GCOV executable" FORCE)
 
 set(CMAKE_CXX_FLAGS_ASAN
     "${CMAKE_CXX_FLAGS_ASAN} -Wno-maybe-uninitialized"