configure.ac: join the cargo-cult of _cv_
configure.ac: join the cargo-cult of _cv_

For some reason, the setting of g_atomic_lock_free wasn't making it down
to the lower part of the configure script where glibconfig.h was being
generated when building using mingw32-configure.

If we prefix glib_cv_ to the start of the variable name (like everyone
else is doing) then it magically starts working.

I love you, automake.

MathieuDuponchelle/glib,lukasz-skalski/glib,johne53/MB3Glib,justinkb/aosp-bluez.glib,bluez-android/glib,gale320/glib,cosimoc/glib,antono/glib,pstglia/external-bluetooth-glib,johne53/MB3Glib,tamaskenez/glib,gale320/glib,bluez-android/glib,iConsole/Console-OS_external_bluetooth_glib,pstglia/platform-external-bluetooth-glib,djdeath/glib,lukasz-skalski/glib,MathieuDuponchelle/glib,justinkb/aosp-bluez.glib,tamaskenez/glib,MathieuDuponchelle/glib,iConsole/Console-OS_external_bluetooth_glib,tchakabam/glib,pstglia/platform-external-bluetooth-glib,endlessm/glib,mzabaluev/glib,MathieuDuponchelle/glib,justinkb/aosp-bluez.glib,01org/android-bluez-glib,gale320/glib,Distrotech/glib,pstglia/external-bluetooth-glib,krichter722/glib,djdeath/glib,tamaskenez/glib,djdeath/glib,pstglia/platform-external-bluetooth-glib,bluez-android/glib,johne53/MB3Glib,endlessm/glib,cosimoc/glib,bluez-android/glib,krichter722/glib,krichter722/glib,pstglia/external-bluetooth-glib,johne53/MB3Glib,antono/glib,antono/glib,gale320/glib,01org/android-bluez-glib,gale320/glib,tchakabam/glib,Distrotech/glib,djdeath/glib,pstglia/platform-external-bluetooth-glib,cention-sany/glib,darren-clark/android_platform_external_bluetooth_glib,pstglia/platform-external-bluetooth-glib,cention-sany/glib,tamaskenez/glib,cention-sany/glib,krichter722/glib,mzabaluev/glib,mzabaluev/glib,endlessm/glib,antono/glib,01org/android-bluez-glib,lukasz-skalski/glib,ieei/glib,Distrotech/glib,ieei/glib,ieei/glib,darren-clark/android_platform_external_bluetooth_glib,mzabaluev/glib,darren-clark/android_platform_external_bluetooth_glib,lukasz-skalski/glib,cosimoc/glib,iConsole/Console-OS_external_bluetooth_glib,ieei/glib,johne53/MB3Glib,djdeath/glib,ieei/glib,pstglia/external-bluetooth-glib,cosimoc/glib,tchakabam/glib,iConsole/Console-OS_external_bluetooth_glib,endlessm/glib,darren-clark/android_platform_external_bluetooth_glib,bluez-android/glib,iConsole/Console-OS_external_bluetooth_glib,01org/android-bluez-glib,MathieuDuponchelle/glib,pstglia/external-bluetooth-glib,tchakabam/glib,tchakabam/glib,justinkb/aosp-bluez.glib,mzabaluev/glib,justinkb/aosp-bluez.glib,lukasz-skalski/glib,krichter722/glib,endlessm/glib,cention-sany/glib,Distrotech/glib,01org/android-bluez-glib,johne53/MB3Glib,cosimoc/glib,darren-clark/android_platform_external_bluetooth_glib,tamaskenez/glib,cention-sany/glib,Distrotech/glib