fix: Allow for environment override of CMAKE_CXX_FLAGS

* Allow for CMAKE_CXX_FLAGS to use its default behavior of taking
  the value of CXXFLAGS if it exists in the environment.
   - c.f. https://cmake.org/cmake/help/v3.31/envvar/CXXFLAGS.html
   - Set CMAKE_CXX_FLAGS and then determine all other compiler or linker
     flags.
* Remove subtractive behavior of removing compiler flags and instead
  use additive behavior. This both makes the user more responsible
  for their flag choices and ensures that known required flags
  can be added without interfering as repeated flags are safe.
* Set range of compatible CMake versions to allow more modern CMake
  to be used if available.
   - Bump lower bound on CMake to v3.12 when this feature was added.
   - c.f. https://cmake.org/cmake/help/latest/command/cmake_minimum_required.html
* Correct typos:
   - 'CMAKE_INSTALL_INCLUDE_DIR' -> 'CMAKE_INSTALL_INCLUDEDIR'
* Add pixi ignores to .gitignore.

.gitignore

@@ -51,4 +51,7 @@ src/qcdloop/config.h
 src/qcdloop/stamp-h1
 examples/cache_test
 examples/cmass_test
-examples/trigger_test
+examples/trigger_test
+# pixi environments
+.pixi
+*.egg-info

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required (VERSION 3.0.2)
+cmake_minimum_required(VERSION 3.12...3.31)
 
 # Disable the use of RPATHS - we probably are not
 # that interested in relocatable binaries and it
@@ -20,37 +20,37 @@ set(CMAKE_CXX_STANDARD 11)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
 set(VERSION 2.0.10)
-include(CheckCXXCompilerFlag)
-if (${CMAKE_CXX_COMPILER_ID} MATCHES "GNU")
-  set(CXX_FLAGS_TO_CHECK "-Wall -Wextra -fvisibility-inlines-hidden -fmessage-length=0 -ftree-vectorize -fstack-protector-strong -O2 -pipe -fext-numeric-literals")
-  set(CXX_FLAGS_DEBUG_TO_CHECK "${CMAKE_CXX_FLAGS_DEBUG} -fsanitize=address ${CMAKE_CXX_FLAGS_TO_CHECK}")
-  set(CMAKE_EXE_LINKER_FLAGS_DEBUG "-fsanitize=address")
-else()
-  set(CXX_FLAGS_TO_CHECK "-Wall -Wextra")
-  set(CXX_FLAGS_DEBUG_TO_CHECK "${CMAKE_CXX_FLAGS_DEBUG} -fsanitize=address ${CMAKE_CXX_FLAGS_TO_CHECK}")
-endif()
-set(CXX_FLAGS_PASSED )
-set(CXX_FLAGS_DEBUG_PASSED )
-foreach(fl ${CXX_FLAGS_TO_CHECK})
-  CHECK_CXX_COMPILER_FLAG(${fl} COMPILER_SUPPORTS_${fl})
-  if(COMPILER_SUPPORTS_${fl})
-    set(CXX_FLAGS_PASSED "${CXX_FLAGS_PASSED} ${fl}" )
+
+# Set default CXXFLAGS but allow for environment override
+# c.f. https://cmake.org/cmake/help/v3.31/envvar/CXXFLAGS.html
+if (NOT CMAKE_CXX_FLAGS)
+  # c.f. https://cmake.org/cmake/help/latest/variable/CMAKE_LANG_COMPILER_ID.html
+  if (${CMAKE_CXX_COMPILER_ID} MATCHES "GNU")
+    set(CMAKE_CXX_FLAGS "-Wall -Wextra -fvisibility-inlines-hidden -fmessage-length=0 -ftree-vectorize -fstack-protector-strong -O2 -pipe -fext-numeric-literals")
+  else()
+    set(CMAKE_CXX_FLAGS "-Wall -Wextra")
   endif()
-endforeach()
-foreach(fl ${CXX_FLAGS_DEBUG_TO_CHECK})
-  CHECK_CXX_COMPILER_FLAG(${fl} COMPILER_SUPPORTS_${fl})
-  if(COMPILER_SUPPORTS_${fl})
-    set(CXX_FLAGS_DEBUG_PASSED "${CXX_FLAGS_DEBUG_PASSED} ${fl}" )
+else()
+  if (${CMAKE_CXX_COMPILER_ID} MATCHES "GNU")
+    # Ensure -fext-numeric-literals is in CMAKE_CXX_FLAGS
+    string(FIND "${CMAKE_CXX_FLAGS}" "-fext-numeric-literals" _found_ext_numeric_literals)
+    if (_found_ext_numeric_literals EQUAL -1)
+      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fext-numeric-literals" CACHE STRING "Update environment CXXFLAGS" FORCE)
+    endif()
   endif()
-endforeach()
-set(CMAKE_CXX_FLAGS ${CXX_FLAGS_PASSED})
-set(CMAKE_CXX_FLAGS_DEBUG ${CXX_FLAGS_DEBUG_PASSED})
-message(STATUS "CMAKE_CXX_FLAGS=${CMAKE_CXX_FLAGS}")
-message(STATUS "CMAKE_CXX_FLAGS_DEBUG=${CMAKE_CXX_FLAGS_DEBUG}")
+endif()
+
+# TODO: QCDLoop is currently only well tested on GNU, so other compiler
+# and linker defaults should be added as they become known
+if (${CMAKE_CXX_COMPILER_ID} MATCHES "GNU")
+  set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -fsanitize=address ${CMAKE_CXX_FLAGS}" CACHE STRING "debug CXXFLAGS" FORCE)
+  set(CMAKE_EXE_LINKER_FLAGS_DEBUG "${CMAKE_EXE_LINKER_FLAGS_DEBUG} -fsanitize=address" CACHE STRING "debug linker flags" FORCE)
+endif()
+
 set(prefix ${CMAKE_INSTALL_PREFIX})
 set(exec_prefix ${CMAKE_INSTALL_PREFIX})
-set(includedir "${CMAKE_INSTALL_INCLUDE_DIR}")
-set(libdir "${CMAKE_INSTALL_LIBDIR}")
+set(includedir ${CMAKE_INSTALL_INCLUDEDIR})
+set(libdir ${CMAKE_INSTALL_LIBDIR})
 
 configure_file(
   "${PROJECT_SOURCE_DIR}/src/qcdloop/config.h.in"
@@ -75,6 +75,7 @@ find_library(QUADMATH_LIBRARY
         /usr/local/lib /usr/x86_64-linux-gnu/*
         /usr/lib/gcc/x86_64-linux-gnu/*
         /usr/lib/gcc/x86_64-redhat-linux/*
+        "${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}"
 )
 
 if(QUADMATH_LIBRARY)