AsmParser: cleanup diagnostics for .rep/.rept

Avoid double diagnostics for invalid expressions for count.  Improve caret
location for negative count.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198099 91177308-0d34-0410-b5e6-96231b3b80d8

test/MC/AsmParser/directive_rept-diagnostics.s

@@ -0,0 +1,41 @@
+# RUN: not llvm-mc -triple i686-elf -filetype asm -o /dev/null %s 2>&1 \
+# RUN:   | FileCheck %s
+
+	.data
+
+	.global invalid_expression
+	.type invalid_expression,@object
+invalid_expression:
+	.rept *
+
+# CHECK: error: unknown token in expression
+# CHECK: 	.rept *
+# CHECK:              ^
+
+	.global bad_token
+	.type bad_token,@object
+bad_token:
+	.rept bad_token
+
+# CHECK: error: unexpected token in '.rept' directive
+# CHECK: 	.rept bad_token
+# CHECK:              ^
+
+	.global negative
+	.type negative,@object
+negative:
+	.rept -32
+
+# CHECK: error: Count is negative
+# CHECK: 	.rept -32
+# CHECK:              ^
+
+	.global trailer
+	.type trailer,@object
+trailer:
+	.rep 0 trailer
+
+# CHECK: error: unexpected token in '.rep' directive
+# CHECK: 	.rep 0 trailer
+# CHECK:               ^
+