build: Check unw_init_local() with custom test.

The most popular, HP's implementation of libunwind doesn't provide the
unw_init_local() symbol by that name (the actual symbol is
`_ULx86_64_init_local`), so it can fail the AC_CHECK_LIB test.

Since there is no symbol that we can portably test with AC_CHECK_LIB on
libunwind, remove the macro call altogether and favor the test program
that I have introduced in 924aa4d.

This fixes a regression from commit
de6de25.

Note: There're two common implementations of libunwind. One is from HP
and the other is from LLVM.

Signed-off-by: Kang-Che Sung <explorer09@gmail.com>

Author: Explorer09

CRT.c

@@ -29,7 +29,7 @@ in the source distribution for its full text.
 #include <sys/mman.h>
 #endif
 
-#if defined(HAVE_LIBUNWIND) && defined(HAVE_LOCAL_UNWIND)
+#if defined(HAVE_LIBUNWIND_H) && defined(HAVE_LOCAL_UNWIND)
 # define PRINT_BACKTRACE
 # define UNW_LOCAL_ONLY
 # include <libunwind.h>
@@ -1346,7 +1346,7 @@ void CRT_setColors(int colorScheme) {
 
 #ifdef PRINT_BACKTRACE
 static void print_backtrace(void) {
-#if defined(HAVE_LIBUNWIND) && defined(HAVE_LOCAL_UNWIND)
+#if defined(HAVE_LIBUNWIND_H) && defined(HAVE_LOCAL_UNWIND)
    unw_context_t context;
    unw_getcontext(&context);
 

configure.ac

@@ -948,33 +948,32 @@ case "$enable_unwind" in
          AC_CHECK_LIB([lzma], [lzma_index_buffer_decode])
       fi
 
-      AC_CHECK_LIB(
-         [unwind],
-         [unw_init_local],
-         [],
-         [
-            if test "$enable_unwind" = yes; then
-               AC_MSG_ERROR([can not find required library libunwind])
-            fi
-            enable_unwind=no
-         ]
-      )
+      if htop_search_header_dir libunwind.h "/usr/include/libunwind"; then
+         AC_DEFINE([HAVE_LIBUNWIND_H], 1, [Define to 1 if you have the <libunwind.h> header file.])
+      elif test "$enable_unwind" = yes; then
+         AC_MSG_ERROR([can not find required header file libunwind.h])
+      else
+         enable_unwind=no
+      fi
       ;;
    *)
       AC_MSG_ERROR([bad value '$enable_unwind' for --enable-unwind])
       ;;
 esac
 
-if test "$enable_unwind" = no; then
-   :
-elif htop_search_header_dir libunwind.h "/usr/include/libunwind"; then
+if test "$enable_unwind" != no; then
    htop_save_CPPFLAGS=$CPPFLAGS
+   htop_save_LIBS=$LIBS
    CPPFLAGS="$AM_CPPFLAGS $CPPFLAGS"
+   LIBS="-lunwind $LIBS"
 
-   AC_MSG_CHECKING([whether local unwinding works])
+   # unw_init_local() is a macro in HP's implemention of libunwind
+   # (the most popular one, Mosberger et al.)
+   AC_MSG_CHECKING([whether -lunwind supports local unwinding])
    AC_LINK_IFELSE(
       [AC_LANG_PROGRAM(
          [[
+#define UNW_LOCAL_ONLY
 #include <libunwind.h>
          ]], [[
          /* If libunwind is built with remote unwinding only,
@@ -1013,21 +1012,23 @@ elif htop_search_header_dir libunwind.h "/usr/include/libunwind"; then
             if test "$enable_unwind" = yes; then
                AC_MSG_WARN([this build of libunwind might not support local unwinding])
             else
+               LIBS=$htop_save_LIBS
                enable_unwind=no
             fi
          fi
       ],
       [
          AC_MSG_RESULT([no])
-         AC_MSG_FAILURE([there are problems with libunwind.h])
+         if test "$enable_unwind" = yes; then
+            AC_MSG_FAILURE([can not link with libunwind])
+         else
+            LIBS=$htop_save_LIBS
+            enable_unwind=no
+         fi
       ]
    )
 
    CPPFLAGS=$htop_save_CPPFLAGS
-elif test "$enable_unwind" = yes; then
-   AC_MSG_ERROR([can not find required header file libunwind.h])
-else
-   enable_unwind=no
 fi
 
 if test "$enable_unwind" != no; then