[clang-tidy] fix buildbot hicpp-signed-bitwise

[JonasToth]

Summary

using signed char instead of plain char, as suggested by alex.

Sorry for breaking and not dealing with this issue. I did not notice it and since these
are my first commits, I am not used to the general workflow.
I hope this fixes the issue and can be commited fast.

[aaron.ballman]

LGTM! FYI: you don't need a review to fix broken build bots unless the commit is something that's really not trivial.

test/clang-tidy/hicpp-signed-bitwise.cpp

 StreamClass &operator>>(StreamClass &os, unsigned int i) {
   return os;
 }
 StreamClass &operator>>(StreamClass &os, int i) {
   return os;
 }
 struct AnotherStream {
   AnotherStream &operator<<(unsigned char c) { return *this; }
-  AnotherStream &operator<<(char c) { return *this; }
+  AnotherStream &operator<<(signed char c) { return *this; }
 
   AnotherStream &operator>>(unsigned char c) { return *this; }
-  AnotherStream &operator>>(char c) { return *this; }
+  AnotherStream &operator>>(signed char c) { return *this; }
 };
 
 void binary_bitwise() {
   int SValue = 42;
   int SResult;
 
   unsigned int UValue = 42;
   unsigned int UResult;
void binary_bitwise() {
   UResult = SValue & -1;
   // CHECK-MESSAGES: :[[@LINE-1]]:13: warning: use of a signed integer operand with a binary bitwise operator
 
   UResult = UValue & 1u;     // Ok
   UResult = UValue & UValue; // Ok
 
   unsigned char UByte1 = 0u;
   unsigned char UByte2 = 16u;
-  char SByte1 = 0;
-  char SByte2 = 16;
+  signed char SByte1 = 0;
+  signed char SByte2 = 16;
 
   UByte1 = UByte1 & UByte2; // Ok
   UByte1 = SByte1 & UByte2;
   // CHECK-MESSAGES: :[[@LINE-1]]:12: warning: use of a signed integer operand with a binary bitwise operator
   UByte1 = SByte1 & SByte2;
   // CHECK-MESSAGES: :[[@LINE-1]]:12: warning: use of a signed integer operand with a binary bitwise operator
   SByte1 = SByte1 & SByte2;
   // CHECK-MESSAGES: :[[@LINE-1]]:12: warning: use of a signed integer operand with a binary bitwise operator
void binary_bitwise() {
 
   int SignedInt1 = 1 << 12;
   // CHECK-MESSAGES: :[[@LINE-1]]:20: warning: use of a signed integer operand with a binary bitwise operator
   int SignedInt2 = 1u << 12;
   // CHECK-MESSAGES: :[[@LINE-1]]:20: warning: use of a signed integer operand with a binary bitwise operator
 }
 
 void f1(unsigned char c) {}
-void f2(char c) {}
+void f2(signed char c) {}
 void f3(int c) {}
 
 void unary_bitwise() {
   unsigned char UByte1 = 0u;
-  char SByte1 = 0;
+  signed char SByte1 = 0;
 
   UByte1 = ~UByte1; // Ok
   SByte1 = ~UByte1;
   SByte1 = ~SByte1;
   // CHECK-MESSAGES: :[[@LINE-1]]:12: warning: use of a signed integer operand with a unary bitwise operator
   UByte1 = ~SByte1;
   // CHECK-MESSAGES: :[[@LINE-1]]:12: warning: use of a signed integer operand with a unary bitwise operator
 
void streams_should_work() {
   StreamClass s;
   s << 1u; // Ok
   s << 1;  // Ok
   s >> 1;  // Ok
   s >> 1u; // Ok
 
   AnotherStream as;
   unsigned char uc = 1u;
-  char sc = 1;
+  signed char sc = 1;
   as << uc; // Ok
   as << sc; // Ok
   as >> uc; // Ok
   as >> sc; // Ok
 }
 
 enum OldEnum {
   ValueOne,