Disable nested function tests for clang

Clang does not support nested functions, and there are no plans to
change this.  This commit disables the three nested function tests
when using clang.

gdb/testsuite/ChangeLog:

	* gdb.base/nested-subp1.exp: Disable test when using clang.
	* gdb.base/nested-subp2.exp: Likewise.
	* gdb.base/nested-subp3.exp: Likewise.

gdb/testsuite/ChangeLog

@@ -1,3 +1,9 @@
+2020-04-20  Gary Benson <gbenson@redhat.com>
+
+	* gdb.base/nested-subp1.exp: Disable test when using clang.
+	* gdb.base/nested-subp2.exp: Likewise.
+	* gdb.base/nested-subp3.exp: Likewise.
+
 2020-04-20  Gary Benson <gbenson@redhat.com>
 
 	* gdb.cp/exception.cc: Fix compilation error with clang.

gdb/testsuite/gdb.base/nested-subp1.exp

@@ -24,6 +24,12 @@ standard_testfile
 
 set testcase "nested-subp1"
 
+get_compiler_info
+if { [test_compiler_info "clang-*"] } {
+    untested "compiler does not support nested functions"
+    return -1
+}
+
 if { [gdb_compile "${srcdir}/${subdir}/${testcase}.c" \
                   [standard_output_file "${testcase}"] \
                   executable \

gdb/testsuite/gdb.base/nested-subp2.exp

@@ -24,6 +24,12 @@ standard_testfile
 
 set testcase "nested-subp2"
 
+get_compiler_info
+if { [test_compiler_info "clang-*"] } {
+    untested "compiler does not support nested functions"
+    return -1
+}
+
 if { [gdb_compile "${srcdir}/${subdir}/${testcase}.c" \
                   [standard_output_file "${testcase}"] \
                   executable \

gdb/testsuite/gdb.base/nested-subp3.exp

@@ -24,6 +24,12 @@ standard_testfile
 
 set testcase "nested-subp3"
 
+get_compiler_info
+if { [test_compiler_info "clang-*"] } {
+    untested "compiler does not support nested functions"
+    return -1
+}
+
 if { [gdb_compile "${srcdir}/${subdir}/${testcase}.c" \
                   [standard_output_file "${testcase}"] \
                   executable \