PGI-Fortran: Add -Mipa=fast,inline as IPO option.

Remove -Mipa=fast as a default flag and add it as an option instead.
-Mipa=fast is a flag that speeds up runtime but at the cost of significant
compile time increase and therefore, shouldn't be a default flag.
In addition, -Mipa isn't supported on PGI OpenPOWER or x86/llvm compilers.

Modules/Compiler/PGI.cmake

@@ -19,16 +19,20 @@ macro(__compiler_pgi lang)
   string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -g -O0")
   string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -O2 -s")
   string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -fast -O3")
-  # -Mipa was dropped with PGI 16.3 from Windows versions
-  if(NOT CMAKE_HOST_WIN32 OR CMAKE_${lang}_COMPILER_VERSION VERSION_LESS 16.3)
-    string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -Mipa=fast")
-  endif()
   string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -O2 -gopt")
 
   if(CMAKE_HOST_WIN32)
     string(APPEND CMAKE_${lang}_FLAGS_INIT " -Bdynamic")
   endif()
 
+  set(_CMAKE_${lang}_IPO_SUPPORTED_BY_CMAKE YES)
+  if(NOT CMAKE_SYSTEM_PROCESSOR STREQUAL ppc64le AND (NOT CMAKE_HOST_WIN32 OR CMAKE_${lang}_COMPILER_VERSION VERSION_LESS 16.3))
+    set(_CMAKE_${lang}_IPO_MAY_BE_SUPPORTED_BY_COMPILER YES)
+    set(CMAKE_${lang}_COMPILE_OPTIONS_IPO "-Mipa=fast,inline")
+  else()
+    set(_CMAKE_${lang}_IPO_MAY_BE_SUPPORTED_BY_COMPILER NO)
+  endif()
+
   # Preprocessing and assembly rules.
   set(CMAKE_${lang}_CREATE_PREPROCESSED_SOURCE "<CMAKE_${lang}_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -E <SOURCE> > <PREPROCESSED_SOURCE>")
   set(CMAKE_${lang}_CREATE_ASSEMBLY_SOURCE "<CMAKE_${lang}_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -S <SOURCE> -o <ASSEMBLY_SOURCE>")