Turbostat: confine AC_COMPILE_IFELSE() inside a AC_CACHE_CHECK block

The previous way of doing worked as expected, but didn't print out
anything in the summary, making it difficult to know why the plugin
wasn't built on older systems.

diff --git a/configure.ac b/configure.ac
index 2ef82ee13606ddf50b7a3d39516eb8888ec79afe..90420f8dc1ab93b812b5abe6b67e8b80522d238a 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -593,10 +593,23 @@ AC_CHECK_HEADERS(termios.h, [have_termios_h="yes"])
 have_asm_msrindex_h="no"
 AC_CHECK_HEADERS(asm/msr-index.h, [have_asm_msrindex_h="yes"])
 
-have_usable_asm_msrindex_h="no"
 if test "x$have_asm_msrindex_h" = "xyes"
 then
-       AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include<asm/msr-index.h>]],[[int y = MSR_CORE_C3_RESIDENCY;]])], [have_usable_asm_msrindex_h="yes"])
+  AC_CACHE_CHECK([whether asm/msr-index.h has MSR_CORE_C3_RESIDENCY],
+                 [c_cv_have_usable_asm_msrindex_h],
+                 AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
+[[[
+#include<asm/msr-index.h>
+]]],
+[[[
+int y = MSR_CORE_C3_RESIDENCY;
+return(y);
+]]]
+  )],
+                 [c_cv_have_usable_asm_msrindex_h="yes"],
+                 [c_cv_have_usable_asm_msrindex_h="no"],
+                                  )
+                 )
 fi
 
 have_cpuid_h="no"
@@ -5199,7 +5212,7 @@ then
        then
                plugin_ipvs="yes"
        fi
-       if test "x$have_usable_asm_msrindex_h" = "xyes" && test "x$have_cpuid_h" = "xyes"
+       if test "x$c_cv_have_usable_asm_msrindex_h" = "xyes" && test "x$have_cpuid_h" = "xyes"
        then
                plugin_turbostat="yes"
        fi