improve clang support (4)

[Bruno Haible]

clang defines __OPTIMIZE__ to 1 when optimizing, like GCC.

Also, it's unlikely that when clang implements __attribute__((__warning__...)),
it will exhibit the same bug as GCC
<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43881>.


2020-08-06  Bruno Haible  <bruno@clisp.org>

        Consider that clang defines __OPTIMIZE__ like GCC does.
        * lib/streq.h: Define the inline functions also on clang.
        * lib/c-strcaseeq.h: Likewise.
        * lib/c++defs.h (_GL_CXXALIASWARN_2, _GL_CXXALIASWARN1_2): Don't enable
        the GCC workaround to clang.

diff --git a/lib/c++defs.h b/lib/c++defs.h
index 402cae4..75d6250 100644
--- a/lib/c++defs.h
+++ b/lib/c++defs.h
@@ -268,7 +268,7 @@
    _GL_CXXALIASWARN_2 (func, namespace)
 /* To work around GCC bug <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43881>,
    we enable the warning only when not optimizing.  */
-# if !__OPTIMIZE__
+# if !(defined __GNUC__ && !defined __clang__ && __OPTIMIZE__)
 #  define _GL_CXXALIASWARN_2(func,namespace) \
     _GL_WARN_ON_USE (func, \
                      "The symbol ::" #func " refers to the system function. " \
@@ -296,7 +296,7 @@
    _GL_CXXALIASWARN1_2 (func, rettype, parameters_and_attributes, namespace)
 /* To work around GCC bug <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43881>,
    we enable the warning only when not optimizing.  */
-# if !__OPTIMIZE__
+# if !(defined __GNUC__ && !defined __clang__ && __OPTIMIZE__)
 #  define 
_GL_CXXALIASWARN1_2(func,rettype,parameters_and_attributes,namespace) \
     _GL_WARN_ON_USE_CXX (func, rettype, parameters_and_attributes, \
                          "The symbol ::" #func " refers to the system 
function. " \
diff --git a/lib/c-strcaseeq.h b/lib/c-strcaseeq.h
index 3c33b6e..897dc99 100644
--- a/lib/c-strcaseeq.h
+++ b/lib/c-strcaseeq.h
@@ -27,7 +27,7 @@
 
 /* Help GCC to generate good code for string comparisons with
    immediate strings. */
-#if defined (__GNUC__) && defined (__OPTIMIZE__)
+#if (defined __GNUC__ || defined __clang__) && defined __OPTIMIZE__
 
 /* Case insensitive comparison of ASCII characters.  */
 # if C_CTYPE_ASCII
diff --git a/lib/streq.h b/lib/streq.h
index cf15c0d..978267b 100644
--- a/lib/streq.h
+++ b/lib/streq.h
@@ -29,7 +29,7 @@
 
 /* Help GCC to generate good code for string comparisons with
    immediate strings. */
-#if defined (__GNUC__) && defined (__OPTIMIZE__)
+#if (defined __GNUC__ || defined __clang__) && defined __OPTIMIZE__
 
 static inline int
 streq9 (const char *s1, const char *s2)