Explicitly specify PROGSUFFIX when compiling final binary (#3918)

Resolves #3906

HISTORY.rst

@@ -19,6 +19,7 @@ PlatformIO Core 5
   - Support debugging on Windows using Windows CMD/CLI (`pio debug <https://docs.platformio.org/page/core/userguide/cmd_debug.html>`__) (`issue #3793 <https://github.com/platformio/platformio-core/issues/3793>`_)
   - Configure a custom pattern to determine when debugging server is started with a new `debug_server_ready_pattern <https://docs.platformio.org/page/projectconf/section_env_debug.html#debug-server-ready-pattern>`__ option
   - Fixed an issue with silent hanging when a custom debug server is not found (`issue #3756 <https://github.com/platformio/platformio-core/issues/3756>`_)
+  - Fixed an issue with broken binary file extension when a custom ``PROGNAME`` contains dot symbols (`issue #3906 <https://github.com/platformio/platformio-core/issues/3906>`_)
 
 * **Static Code Analysis**
 

platformio/builder/tools/platformio.py

@@ -75,7 +75,7 @@ def BuildProgram(env):
         env.Append(_LIBFLAGS=" -Wl,--end-group")
 
     program = env.Program(
-        os.path.join("$BUILD_DIR", env.subst("$PROGNAME")), env["PIOBUILDFILES"]
+        os.path.join("$BUILD_DIR", env.subst("$PROGNAME$PROGSUFFIX")), env["PIOBUILDFILES"]
     )
     env.Replace(PIOMAINPROG=program)