cmake config tests FAST_BUILD variable

[discopt]

The generated (and installed) highs-config.make file contains a test

if (FAST_BUILD)
  if(NOT TARGET highs)
    include("${CMAKE_CURRENT_LIST_DIR}/highs-targets.cmake")
  endif()
  set(HIGHS_LIBRARIES highs)
else()
  if(NOT TARGET libhighs)
    include("${CMAKE_CURRENT_LIST_DIR}/highs-targets.cmake")
  endif()
  set(HIGHS_LIBRARIES highs)
endif()

This file is included from cmake projects that use HiGHS. So they typically don't have a FAST_BUILD variable. Even if they have one, it may be different from the value that this variable had when building HiGHS. I don't know exactly what the difference between FAST_BUILD and non-FAST_BUILD is, but I guess the intended behavior would be to have @FAST_BUILD@ in the if-statement.

[galabovaa]

Thank you! We intend to remove FAST_BUILD but until then I have added your suggestion in #1744