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 2ef82ee..90420f8 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