build(windows): Enable segment heap if possible (#7142)

With Visual Studio 2026 18.6, Microsoft included a script to easily
enable the segment heap for apps
([blog](https://devblogs.microsoft.com/cppblog/segment-heap-support-for-c-projects-in-visual-studio/)).
The segment heap was already available for some years, but it hasn't
been enabled by default. With the provided script we can add a manifest
to enable it. In my basic testing it reduced the memory usage from
~75MiB to ~70MiB with one tab and 4 messages. So it should be a free win
for us.

Reviewed-by: pajlada <rasmus.karlsson@pajlada.com>

CMakeLists.txt

@@ -15,6 +15,10 @@ list(APPEND CMAKE_MODULE_PATH
     "${CMAKE_SOURCE_DIR}/cmake"
     )
 
+if(WIN32 AND NOT MINGW)
+    include(EnableSegmentHeap)
+endif()
+
 option(BUILD_APP "Build Chatterino" ON)
 option(BUILD_TESTS "Build the tests for Chatterino" OFF)
 option(BUILD_BENCHMARKS "Build the benchmarks for Chatterino" OFF)

cmake/EnableSegmentHeap.cmake

@@ -0,0 +1,17 @@
+# SPDX-FileCopyrightText: 2026 Contributors to Chatterino <https://chatterino.com>
+#
+# SPDX-License-Identifier: CC0-1.0
+
+if(NOT DEFINED ENV{VSINSTALLDIR})
+    message(WARNING "Missing VSINSTALLDIR environment variable - not enabling segment heap.")
+    return()
+endif()
+
+set(segment_heap_path "$ENV{VSINSTALLDIR}Common7/IDE/CommonExtensions/Microsoft/CMake/cmake/Microsoft/SegmentHeap.cmake")
+if (NOT EXISTS "${segment_heap_path}")
+    message(STATUS "Missing '${segment_heap_path}'. Segment heap will be disabled - consider updating Visual Studio.")
+    return()
+endif()
+
+message(STATUS "Including segment heap script from '${segment_heap_path}'.")
+include("${segment_heap_path}")