last chunk: fix build with reentrant qhull

https://salsa.debian.org/science-team/plplot/-/blob/master/debian/patches/reentrant-qhull.patch

Index: cmake/modules/csiro.cmake
--- cmake/modules/csiro.cmake.orig
+++ cmake/modules/csiro.cmake
@@ -30,11 +30,11 @@ if(PL_HAVE_QHULL OR WITH_CSA)
   if(CMAKE_SYSTEM_PROCESSOR MATCHES "i[0-9]86" AND NOT CMAKE_C_COMPILER MATCHES "gcc")
     set(NAN_CFLAGS "${NAN_CFLAGS} -mieee-fp")
   elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "alpha.*")
-    if(CMAKE_C_COMPILER MATCHES "gcc")
+    if(CMAKE_COMPILER_IS_GNUCC)
       set(NAN_CFLAGS "${NAN_CFLAGS} -mieee")
-    else(CMAKE_C_COMPILER MATCHES "gcc")
+    else(CMAKE_COMPILER_IS_GNUCC)
       set(NAN_CFLAGS "${NAN_CFLAGS} -ieee")
-    endif(CMAKE_C_COMPILER MATCHES "gcc")
+    endif(CMAKE_COMPILER_IS_GNUCC)
   endif(CMAKE_SYSTEM_PROCESSOR MATCHES "i[0-9]86" AND NOT CMAKE_C_COMPILER MATCHES "gcc")
   if(NOT DEFINED NaNAwareCCompiler)
     message(STATUS "Check for NaN awareness in C compiler")
@@ -89,11 +89,7 @@ if(PL_HAVE_QHULL)
       message(STATUS "WARNING: function qh_new_qhull not found.  Setting PL_HAVE_QHULL to OFF.")
       set(PL_HAVE_QHULL OFF CACHE BOOL "Enable use of the Qhull library" FORCE)
     endif(NOT QH_NEW_EXIST)
-    if(HAS_LIBQHULL_INCLUDE)
-      file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/Check_realT_size.c "#include <libqhull/qhull_a.h>")
-    else(HAS_LIBQHULL_INCLUDE)
-      file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/Check_realT_size.c "#include <qhull/qhull_a.h>")
-    endif(HAS_LIBQHULL_INCLUDE)
+    file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/Check_realT_size.c "#include <libqhull_r/qhull_ra.h>")
     file(APPEND ${CMAKE_CURRENT_BINARY_DIR}/Check_realT_size.c
       "
 int main(void)