Detect the presence of malloc_trim to fix the build with musl

malloc_trim is indeed a GNU extension, but an extension of glibc.
Relying on __GNUC__ unfortunately doesn't help with that. Check for
the actual presence of malloc_trim with cmake's check_function_exists
instead.
This fixes the build with musl libc, which doesn't come with
malloc_trim.

Co-authored-by: Ahmad Samir <a.samirh78@gmail.com>

CMakeLists.txt

@@ -94,7 +94,7 @@ set(HAVE_X11 ${X11_FOUND})
 # Check for function GETPWUID
 check_symbol_exists(getpwuid "pwd.h" HAVE_GETPWUID)
 
-check_include_files(malloc.h      HAVE_MALLOC_H)
+check_function_exists(malloc_trim HAVE_MALLOC_TRIM)
 
 # See above includes for defaults
 add_definitions(

src/Screen.cpp

@@ -28,13 +28,11 @@
 #include "history/HistoryType.h"
 #include "profile/Profile.h"
 
-#ifdef HAVE_MALLOC_H
-    // For malloc_trim, which is a GNU extension
-    #ifdef __GNUC__
-    extern "C" {
-            #include <malloc.h>
-    }
-    #endif
+#ifdef HAVE_MALLOC_TRIM
+// For malloc_trim, which is a GNU extension
+extern "C" {
+#include <malloc.h>
+}
 #endif
 
 using namespace Konsole;
@@ -1799,14 +1797,13 @@ void Screen::setScroll(const HistoryType &t, bool copyPreviousScroll)
         t.scroll(_history);
     }
     _graphicsPlacements.clear();
-#ifdef HAVE_MALLOC_H
+#ifdef HAVE_MALLOC_TRIM
+
 #ifdef Q_OS_LINUX
-#ifdef __GNUC__
     // We might have been using gigabytes of memory, so make sure it is actually released
     malloc_trim(0);
 #endif
 #endif
-#endif
 }
 
 bool Screen::hasScroll() const

src/config-konsole.h.cmake

@@ -15,5 +15,5 @@
 
 #cmakedefine HAVE_GETPWUID ${HAVE_GETPWUID}
 
-/* Define to 1 if you have the <malloc.h> header file. */
-#cmakedefine HAVE_MALLOC_H 1
+/* Defined if system has the malloc_trim function, which is a GNU extension */
+#cmakedefine HAVE_MALLOC_TRIM