Bug 1718408 - Enable some clang warning flags that are currently warning-free. r=firefox-build-system-reviewers,andi

-Wdeprecated-this-capture (in a lambda expression)
warning: implicit capture of ‘this’ with a capture default of ‘=’ is deprecated
https://clang.llvm.org/docs/DiagnosticsReference.html#wdeprecated-this-capture

-Wenum-compare-conditional
Example: return foo ? enumType1 : enumType2; // deprecated in C++20
https://clang.llvm.org/docs/DiagnosticsReference.html#wenum-compare-conditional

-Wformat-type-confusion (in a sprintf-like format function)
warning: format specifies type A (e.g. short) but the argument has type B (e.g. char)
https://clang.llvm.org/docs/DiagnosticsReference.html#wformat-type-confusion

-Wshadow-uncaptured-local (variable declared in a lambda expression)
warning: declaration shadows a local variable
warning: declaration shadows a variable in C
warning: declaration shadows a static data member of C
warning: declaration shadows a field of C
warning: declaration shadows a typedef in C
warning: declaration shadows a type alias in C
warning: declaration shadows a structured binding
https://clang.llvm.org/docs/DiagnosticsReference.html#wshadow-uncaptured-local

Differential Revision: https://phabricator.services.mozilla.com/D118896

build/moz.configure/warnings.configure

@@ -40,9 +40,15 @@ add_gcc_warning("-Wall")
 # catch implicit truncation of enum values assigned to smaller bit fields
 check_and_add_gcc_warning("-Wbitfield-enum-conversion")
 
+# catches deprecated implicit capture of `this` in lambdas.
+check_and_add_gcc_warning("-Wdeprecated-this-capture", cxx_compiler)
+
 # catches bugs, e.g. "if (c); foo();", few false positives
 add_gcc_warning("-Wempty-body")
 
+# catches mismatched printf integer sizes.
+check_and_add_gcc_warning("-Wformat-type-confusion")
+
 # catches return types with qualifiers like const
 add_gcc_warning("-Wignored-qualifiers")
 
@@ -61,6 +67,9 @@ add_gcc_warning("-Wpointer-arith")
 # catch modifying constructor parameter that shadows member variable
 check_and_add_gcc_warning("-Wshadow-field-in-constructor-modified")
 
+# catches lambda variables shadowing function variables.
+check_and_add_gcc_warning("-Wshadow-uncaptured-local", cxx_compiler)
+
 # catches comparing signed/unsigned ints
 add_gcc_warning("-Wsign-compare")
 
@@ -102,6 +111,9 @@ check_and_add_gcc_warning("-Wcomma", cxx_compiler)
 # catches duplicated conditions in if-else-if chains
 check_and_add_gcc_warning("-Wduplicated-cond")
 
+# catches expessions mixing different enum types deprecated in C++20
+check_and_add_gcc_warning("-Wenum-compare-conditional")
+
 # catches unintentional switch case fallthroughs
 check_and_add_gcc_warning("-Wimplicit-fallthrough", cxx_compiler)