ld/testsuite: skip tests related to -shared when disabled

Call the helper function "check_shared_lib_support" to ensure -shared
is enabled before launching ld-shared, ld-elfweak and ld-elfvers.
This allows to catch custom targets explicitly disabling it.

ld/ChangeLog:

	* testsuite/ld-elfvers/vers.exp: Call check_shared_lib_support.
	* testsuite/ld-elfweak/elfweak.exp: Likewise.
	* testsuite/ld-shared/shared.exp: Likewise.

ld/testsuite/ld-elfvers/vers.exp

@@ -27,6 +27,11 @@ if { ![check_compiler_available] } {
     return
 }
 
+# Skip targets where -shared is not supported
+if { ![check_shared_lib_support] } {
+    return
+}
+
 # This test can only be run on a couple of ELF platforms.
 # Square bracket expressions seem to confuse istarget.
 # This is similar to the test that is used in ld-shared, BTW.

ld/testsuite/ld-elfweak/elfweak.exp

@@ -27,6 +27,11 @@ if { ![check_compiler_available] } {
     return
 }
 
+# Skip targets where -shared is not supported
+if { ![check_shared_lib_support] } {
+    return
+}
+
 # This test can only be run on a couple of ELF platforms.
 # Square bracket expressions seem to confuse istarget.
 # This is similar to the test that is used in ld-shared, BTW.

ld/testsuite/ld-shared/shared.exp

@@ -30,6 +30,11 @@ if { ![check_compiler_available] } {
     return
 }
 
+# Skip targets where -shared is not supported
+if { ![check_shared_lib_support] } {
+    return
+}
+
 # This test can only be run on a couple of ELF platforms.
 # Square bracket expressions seem to confuse istarget.
 if { ![istarget hppa*64*-*-hpux*] \