Introduce "Modern CMake" in FLTK

This is a big commit and there are too many changes to list them all.
The main changes are:

- rename all CMake build options to 'FLTK_*'
- export library targets with namespace (prefix) 'fltk::'
- standardize shared library target names with suffix '-shared'
- set public build properties on libraries for consumers
- document library names and aliases in README.CMake.txt
- document changes in "Migrating Code from FLTK 1.3 to 1.4"
- partial backwards compatibility for old user projects

Included but not directly related changes:

- fix Windows (Visual Studio) DLL build
- add CMake function fl_debug_target() to show target properties
- don't build test programs if FLTK is a subproject
- internal: reformat CMake code: remove space before '('

Thanks to Matthias and Manolo for their help, testing, and feeback.

1 files changed, 4 insertions, 4 deletions

diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index b1265db62..cbb1ecf36 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -36,7 +36,7 @@ jobs:
       # Note the current convention is to use the -S and -B options here to specify source
       # and build directories, but this is only available with CMake 3.13 and higher.
       # The CMake binaries on the Github Actions machines are (as of this writing) 3.12
-      run: cmake $GITHUB_WORKSPACE -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DOPTION_USE_WAYLAND=OFF -DCMAKE_CXX_STANDARD=98 -DCMAKE_CXX_EXTENSIONS=OFF -DCMAKE_C_FLAGS_INIT="-Wall -Wunused" -DCMAKE_CXX_FLAGS_INIT="-Wall -Wunused"
+      run: cmake $GITHUB_WORKSPACE -D CMAKE_BUILD_TYPE=$BUILD_TYPE -D FLTK_OPTION_USE_WAYLAND=OFF -D CMAKE_CXX_STANDARD=98 -D CMAKE_CXX_EXTENSIONS=OFF -D CMAKE_C_FLAGS_INIT="-Wall -Wunused" -D CMAKE_CXX_FLAGS_INIT="-Wall -Wunused"
 
     - name: Build
       working-directory: ${{github.workspace}}/build
@@ -72,7 +72,7 @@ jobs:
       # Note the current convention is to use the -S and -B options here to specify source
       # and build directories, but this is only available with CMake 3.13 and higher.
       # The CMake binaries on the Github Actions machines are (as of this writing) 3.12
-      run: cmake $GITHUB_WORKSPACE -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DCMAKE_CXX_STANDARD=11 -DCMAKE_CXX_EXTENSIONS=OFF -DCMAKE_C_FLAGS_INIT="-Wall -Wunused" -DCMAKE_CXX_FLAGS_INIT="-Wall -Wunused -Wsuggest-override"
+      run: cmake $GITHUB_WORKSPACE -D CMAKE_BUILD_TYPE=$BUILD_TYPE -D CMAKE_CXX_STANDARD=11 -D CMAKE_CXX_EXTENSIONS=OFF -D CMAKE_C_FLAGS_INIT="-Wall -Wunused" -D CMAKE_CXX_FLAGS_INIT="-Wall -Wunused -Wsuggest-override"
 
     - name: Build
       working-directory: ${{github.workspace}}/build
@@ -103,7 +103,7 @@ jobs:
       # Note the current convention is to use the -S and -B options here to specify source
       # and build directories, but this is only available with CMake 3.13 and higher.
       # The CMake binaries on the Github Actions machines are (as of this writing) 3.12
-      run: cmake $GITHUB_WORKSPACE -DCMAKE_BUILD_TYPE=$BUILD_TYPE -DCMAKE_CXX_STANDARD=20 -DCMAKE_CXX_EXTENSIONS=OFF -DCMAKE_C_FLAGS_INIT="-Wall -Wunused" -DCMAKE_CXX_FLAGS_INIT="-Wall -Wunused -Wsuggest-override"
+      run: cmake $GITHUB_WORKSPACE -D CMAKE_BUILD_TYPE=$BUILD_TYPE -D CMAKE_CXX_STANDARD=20 -D CMAKE_CXX_EXTENSIONS=OFF -D CMAKE_C_FLAGS_INIT="-Wall -Wunused" -D CMAKE_CXX_FLAGS_INIT="-Wall -Wunused -Wsuggest-override"
 
     - name: Build
       working-directory: ${{github.workspace}}/build
@@ -130,7 +130,7 @@ jobs:
 
     - name: Configure CMake
       working-directory: ${{github.workspace}}/build
-      run: cmake -D OPTION_USE_SYSTEM_LIBJPEG:BOOL=OFF -D OPTION_USE_SYSTEM_LIBPNG:BOOL=OFF -D OPTION_USE_SYSTEM_ZLIB:BOOL=OFF ..
+      run: cmake -D FLTK_USE_SYSTEM_LIBJPEG:BOOL=OFF -D FLTK_USE_SYSTEM_LIBPNG:BOOL=OFF -D FLTK_USE_SYSTEM_ZLIB:BOOL=OFF ..
 
     - name: Build
       working-directory: ${{github.workspace}}/build