Fix gdb.base/charset.exp with Clang

gdb.base/charset.exp fails to run with Clang, because of:

 gdb compile failed, /home/pedro/gdb/mygit/src/gdb/testsuite/gdb.base/charset.c:144:20: warning:
       implicit conversion from 'int' to 'char' changes value from 162 to -94
       [-Wconstant-conversion]
		11, 162, 17);
		    ^~~
 /home/pedro/gdb/mygit/src/gdb/testsuite/gdb.base/charset.c:151:16: warning:
       implicit conversion from 'int' to 'char' changes value from 167 to -89
       [-Wconstant-conversion]
		167,
		^~~
 /home/pedro/gdb/mygit/src/gdb/testsuite/gdb.base/charset.c:168:16: warning:
       implicit conversion from 'int' to 'char' changes value from 167 to -89
       [-Wconstant-conversion]
		167,
		^~~
 3 warnings generated.

		 === gdb Summary ===

 # of untested testcases         1

Fix it by changing init_string to take unsigned char parameters.

gdb/testsuite/ChangeLog:

	* gdb.base/charset.c (init_string): Change all char parameters to
	unsigned char parameters.

2 files changed, 18 insertions, 4 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 47e4d7c509a..79c1208bd50 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,10 @@
 2020-07-03  Pedro Alves  <palves@redhat.com>
 
+	* gdb.base/charset.c (init_string): Change all char parameters to
+	unsigned char parameters.
+
+2020-07-03  Pedro Alves  <palves@redhat.com>
+
 	* gdb.base/call-sc.exp (start_scalars_test): Use
 	prepare_for_testing and don't try compiling with -DNO_PROTOTYPES.
 	* gdb.base/overlays.c: Remove references to PARAMS.
diff --git a/gdb/testsuite/gdb.base/charset.c b/gdb/testsuite/gdb.base/charset.c
index ec4927da515..20d548b1928 100644
--- a/gdb/testsuite/gdb.base/charset.c
+++ b/gdb/testsuite/gdb.base/charset.c
@@ -77,12 +77,21 @@ short short_array[3];
 int int_array[3];
 long long_array[3];
 
+/* These are unsigned char so we can pass down characters >127 without
+   explicit casts or warnings.  */
+
 void
 init_string (char string[],
-             char x,
-             char alert, char backspace, char form_feed,
-             char line_feed, char carriage_return, char horizontal_tab,
-             char vertical_tab, char cent, char misc_ctrl)
+	     unsigned char x,
+	     unsigned char alert,
+	     unsigned char backspace,
+	     unsigned char form_feed,
+	     unsigned char line_feed,
+	     unsigned char carriage_return,
+	     unsigned char horizontal_tab,
+	     unsigned char vertical_tab,
+	     unsigned char cent,
+	     unsigned char misc_ctrl)
 {
   int i;