CheckSource{Runs,Compiles}: Fix default Fortran source extension

In commit 357e2ef429 (CheckSoureRuns: Add a unified way to check if a
source runs, 2020-09-14, v3.19.0-rc1~118^2), the default Fortran source
file extension was accidentally changed from `.F90` to `.F`.  Fix that.

In commit 10ae907de0 (CheckSoureCompiles: Add a unified way to check if
a source compiles, 2020-09-14, v3.19.0-rc1~118^2~1), the default Fortran
source extension was correctly preserved as `.F`, but `.F90` is a better
default both for consistency and modern usage.  Use that for direct
calls to the `check_source_compiles` macro.  Update our original
`check_fortran_source_compiles` implementation to use `.F` by default
as it did before.

Fixes: #21307

Modules/CheckFortranSourceCompiles.cmake

@@ -90,5 +90,7 @@ include_guard(GLOBAL)
 include(CheckSourceCompiles)
 
 macro(CHECK_Fortran_SOURCE_COMPILES SOURCE VAR)
-  check_source_compiles(Fortran "${SOURCE}" ${VAR} ${ARGN})
+  # Pass the SRC_EXT we used by default historically.
+  # A user-provided SRC_EXT argument in ARGN will override ours.
+  check_source_compiles(Fortran "${SOURCE}" ${VAR} SRC_EXT "F" ${ARGN})
 endmacro()

Modules/CheckFortranSourceRuns.cmake

@@ -86,5 +86,7 @@ include_guard(GLOBAL)
 include(CheckSourceRuns)
 
 macro(CHECK_Fortran_SOURCE_RUNS SOURCE VAR)
-  check_source_runs(Fortran "${SOURCE}" ${VAR} ${ARGN})
+  # Pass the SRC_EXT we used by default historically.
+  # A user-provided SRC_EXT argument in ARGN will override ours.
+  check_source_runs(Fortran "${SOURCE}" ${VAR} SRC_EXT "F90" ${ARGN})
 endmacro()

Modules/CheckSourceCompiles.cmake

@@ -94,7 +94,7 @@ function(CHECK_SOURCE_COMPILES _lang _source _var)
       set(_lang_ext "cu")
     elseif(_lang STREQUAL Fortran)
       set(_lang_textual "Fortran")
-      set(_lang_ext "F")
+      set(_lang_ext "F90")
     elseif(_lang STREQUAL ISPC)
       set(_lang_textual "ISPC")
       set(_lang_ext "ispc")
@@ -121,8 +121,11 @@ function(CHECK_SOURCE_COMPILES _lang _source _var)
     foreach(arg ${ARGN})
       if("${arg}" MATCHES "^(FAIL_REGEX|SRC_EXT)$")
         set(_key "${arg}")
-      elseif(_key)
-        list(APPEND _${_key} "${arg}")
+      elseif(_key STREQUAL "FAIL_REGEX")
+        list(APPEND _FAIL_REGEX "${arg}")
+      elseif(_key STREQUAL "SRC_EXT")
+        set(_SRC_EXT "${arg}")
+        set(_key "")
       else()
         message(FATAL_ERROR "Unknown argument:\n  ${arg}\n")
       endif()

Modules/CheckSourceRuns.cmake

@@ -92,7 +92,7 @@ function(CHECK_SOURCE_RUNS _lang _source _var)
       set(_lang_ext "cu")
     elseif(_lang STREQUAL Fortran)
       set(_lang_textual "Fortran")
-      set(_lang_ext "F")
+      set(_lang_ext "F90")
     elseif(_lang STREQUAL OBJC)
       set(_lang_textual "Objective-C")
       set(_lang_ext "m")
@@ -114,10 +114,13 @@ function(CHECK_SOURCE_RUNS _lang _source _var)
     set(_SRC_EXT)
     set(_key)
     foreach(arg ${ARGN})
-      if("${arg}" MATCHES "^(SRC_EXT)$")
+      if("${arg}" MATCHES "^(FAIL_REGEX|SRC_EXT)$")
         set(_key "${arg}")
-      elseif(_key)
-        list(APPEND _${_key} "${arg}")
+      elseif(_key STREQUAL "FAIL_REGEX")
+        list(APPEND _FAIL_REGEX "${arg}")
+      elseif(_key STREQUAL "SRC_EXT")
+        set(_SRC_EXT "${arg}")
+        set(_key "")
       else()
         message(FATAL_ERROR "Unknown argument:\n  ${arg}\n")
       endif()