From 8887f6c09c27dd5f6dfeecc4c766ec9f67d95f7a Mon Sep 17 00:00:00 2001
From: Kai Blaschke <kai.blaschke@kb-dev.net>
Date: Fri, 13 Sep 2019 19:25:09 +0200
Subject: [PATCH] [libpng] Replace find_library() with a simple set() for
 linking libm on UNIX (#8079)

---
 ports/libpng/CONTROL             |  2 +-
 ports/libpng/fix-libm-unix.patch | 12 ++++++++++++
 ports/libpng/portfile.cmake      |  1 +
 3 files changed, 14 insertions(+), 1 deletion(-)
 create mode 100644 ports/libpng/fix-libm-unix.patch

diff --git a/ports/libpng/CONTROL b/ports/libpng/CONTROL
index c77b2a9d15..bc06e8debd 100644
--- a/ports/libpng/CONTROL
+++ b/ports/libpng/CONTROL
@@ -1,5 +1,5 @@
 Source: libpng
-Version: 1.6.37-3
+Version: 1.6.37-4
 Build-Depends: zlib
 Homepage: https://github.com/glennrp/libpng
 Description: libpng is a library implementing an interface for reading and writing PNG (Portable Network Graphics) format files.
diff --git a/ports/libpng/fix-libm-unix.patch b/ports/libpng/fix-libm-unix.patch
new file mode 100644
index 0000000000..0abd20879e
--- /dev/null
+++ b/ports/libpng/fix-libm-unix.patch
@@ -0,0 +1,12 @@
+diff -ur a/CMakeLists.txt b/CMakeLists.txt
+--- a/CMakeLists.txt	2019-04-14 20:10:32.000000000 +0200
++++ b/CMakeLists.txt	2019-09-06 14:14:39.425498139 +0200
+@@ -44,7 +44,7 @@
+ endif()
+ 
+ if(UNIX AND NOT APPLE AND NOT BEOS AND NOT HAIKU)
+-  find_library(M_LIBRARY m)
++  set(M_LIBRARY m)
+ else()
+   # libm is not needed and/or not available
+   set(M_LIBRARY "")
diff --git a/ports/libpng/portfile.cmake b/ports/libpng/portfile.cmake
index 7e4fc8b042..24858f26c6 100644
--- a/ports/libpng/portfile.cmake
+++ b/ports/libpng/portfile.cmake
@@ -8,6 +8,7 @@ vcpkg_from_github(
     HEAD_REF master
     PATCHES
         use-abort-on-all-platforms.patch
+        fix-libm-unix.patch
 )
 
 if(VCPKG_LIBRARY_LINKAGE STREQUAL dynamic)