liblzma: Use __has_attribute(__symver__) to fix Clang detection.

If someone sets up Clang to define __GNUC__ to 10 or greater
then symvers broke. __has_attribute is supported by such GCC
and Clang versions that don't support __symver__ so this should
be much better and simpler way to detect if __symver__ is
actually supported.

Thanks to Tomasz Gajc for the bug report.

diff --git a/src/liblzma/common/common.h b/src/liblzma/common/common.h
index 7fb1732adff7a4a97b6871a5df75ee0b58fb3955..671d3bc430b875329e2a84f0e1b7a2c348d45742 100644 (file)
--- a/src/liblzma/common/common.h
+++ b/src/liblzma/common/common.h
@@ -34,6 +34,14 @@
 
 #include "lzma.h"
 
+// This is for detecting modern GCC and Clang attributes
+// like __symver__ in GCC >= 10.
+#ifdef __has_attribute
+#      define lzma_has_attribute(attr) __has_attribute(attr)
+#else
+#      define lzma_has_attribute(attr) 0
+#endif
+
 // The extra symbol versioning in the C files may only be used when
 // building a shared library. If HAVE_SYMBOL_VERSIONS_LINUX is defined
 // to 2 then symbol versioning is done only if also PIC is defined.
@@ -63,7 +71,12 @@
 // since 2000). When using @@ instead of @@@, the internal name must not be
 // the same as the external name to avoid problems in some situations. This
 // is why "#define foo_52 foo" is needed for the default symbol versions.
-#      if TUKLIB_GNUC_REQ(10, 0) && !defined(__INTEL_COMPILER)
+//
+// __has_attribute is supported before GCC 10 and it is supported in Clang 14
+// too (which doesn't support __symver__) so use it to detect if __symver__
+// is available. This should be far more reliable than looking at compiler
+// version macros as nowadays especially __GNUC__ is defined by many compilers.
+#      if lzma_has_attribute(__symver__)
 #              define LZMA_SYMVER_API(extnamever, type, intname) \
                        extern __attribute__((__symver__(extnamever))) \
                                        LZMA_API(type) intname