Add CMake commands to build the KPP executable file

src/CMakeLists.txt
- Add CMake commands to define the KPP executable file, where it
  should be installed, and what it depends on.

CHANGELOG.md
- Updated accordingly

Signed-off-by: Bob Yantosca <yantosca@seas.harvard.edu>

CHANGELOG.md

@@ -5,7 +5,13 @@ This file documents all notable changes to the GEOS-Chem Classic wrapper reposit
 - src/HEMCO/CHANGELOG.md
 - src/Cloud-J/CHANGELOG.md
 
-The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/), and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+The format is based on [Keep a
+Changelog](https://keepachangelog.com/en/1.0.0/), and this project
+adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased] - TBD
+### Added
+- Added code to `src/CMakeLists.txt` to build & install the KPP standalone executable when `fullchem` or `custom` mechanisms are selected
 
 ## [14.5.0] - 2024-11-08
 ### Changed

src/CMakeLists.txt

@@ -38,6 +38,33 @@ set_target_properties(${EXE_FILE_NAME}
   RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin
 )
 
+#-----------------------------------------------------------------------------
+# Define the KPP standalone executable:
+# 1. Specify a cache variable with the default target name
+# 2. Specify the location of the main program
+# 3. Specify libraries that the main program depends on
+# 4. Store the binary exectuable file in the bin folder (pre-install)
+#
+# At present build KPP standalone only for fullchem or custom mechanisms.
+#-----------------------------------------------------------------------------
+if("${MECH}" STREQUAL fullchem OR "${MECH}" STREQUAL custom)
+  set(KPPSA_FILE_NAME kpp_standalone CACHE STRING
+    "Default name for the KPP standalone executable file")
+  mark_as_advanced(KPPSA_FILE_NAME)
+
+  add_executable(${KPPSA_FILE_NAME}
+    GEOS-Chem/KPP/standalone/kpp_standalone.F90
+  )
+  target_link_libraries(${KPPSA_FILE_NAME}
+    PUBLIC
+    KPPStandalone
+  )
+  set_target_properties(${KPPSA_FILE_NAME}
+    PROPERTIES
+    RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin
+  )
+endif()
+
 #-----------------------------------------------------------------------------
 # When "make install" is run, copy the target to the destination folder
 # (which is typically one directory higher than the CMake build folder)