[Ada] System.OS_Interface: fix link order on Linux

2019-07-05  Arnaud Charlet  <charlet@adacore.com>

gcc/ada/

	* libgnarl/s-osinte__linux.ads: Link with -lrt before -lpthread.

From-SVN: r273120

gcc/ada/ChangeLog

+2019-07-05  Arnaud Charlet  <charlet@adacore.com>
+
+	* libgnarl/s-osinte__linux.ads: Link with -lrt before -lpthread.
+
 2019-07-05  Ed Schonberg  <schonberg@adacore.com>
 
 	* exp_pakd.adb (Expand_Bit_Packed_Element_Set): Add explicit

gcc/ada/libgnarl/s-osinte__linux.ads

@@ -46,10 +46,11 @@ with System.OS_Constants;
 package System.OS_Interface is
    pragma Preelaborate;
 
-   pragma Linker_Options ("-lpthread");
    pragma Linker_Options ("-lrt");
    --  Needed for clock_getres with glibc versions prior to 2.17
 
+   pragma Linker_Options ("-lpthread");
+
    subtype int            is Interfaces.C.int;
    subtype char           is Interfaces.C.char;
    subtype short          is Interfaces.C.short;