cmake: honor CURL_DISABLE_INSTALL and CURL_ENABLE_EXPORT_TARGET in lib and src

Based on existing code and commit history it appears
`CURL_DISABLE_INSTALL` means to prevent calling `install()`;
`CURL_ENABLE_EXPORT_TARGET` means to prevent calling `export()` and
`install()`s with `EXPORT` in them.

Fix them to also apply to the lib and src directories in that vain:
- lib: honor `CURL_DISABLE_INSTALL`
- src: honor `CURL_DISABLE_INSTALL`
- src: honor `CURL_ENABLE_EXPORT_TARGET`

https://cmake.org/cmake/help/v4.2/command/install.html
https://cmake.org/cmake/help/v4.2/command/export.html

- `CURL_DISABLE_INSTALL` follow-up to:
  aace27b096 #12287
- `CURL_ENABLE_EXPORT_TARGET` follow-up to:
  8698825106 #9638
  643ec29645 #7060

Closes #19144

docs/libcurl/opts/CMakeLists.txt

@@ -28,6 +28,7 @@ include("${CMAKE_CURRENT_BINARY_DIR}/Makefile.inc.cmake")
 curl_add_manual_pages(man_MANS)
 add_custom_target(curl-opts-man DEPENDS ${man_MANS})
 add_dependencies(curl-man curl-opts-man)
+
 if(NOT CURL_DISABLE_INSTALL)
   set(_src "")
   foreach(_file IN LISTS man_MANS)

lib/CMakeLists.txt

@@ -304,7 +304,7 @@ add_library(${LIB_NAME} ALIAS ${LIB_SELECTED})
 add_library(${PROJECT_NAME}::${LIB_NAME} ALIAS ${LIB_SELECTED})
 
 if(CURL_ENABLE_EXPORT_TARGET)
-  if(BUILD_STATIC_LIBS)
+  if(NOT CURL_DISABLE_INSTALL AND BUILD_STATIC_LIBS)
     install(TARGETS ${LIB_STATIC}
       EXPORT ${TARGETS_EXPORT_NAME}
       ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
@@ -312,7 +312,7 @@ if(CURL_ENABLE_EXPORT_TARGET)
       RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
     )
   endif()
-  if(BUILD_SHARED_LIBS)
+  if(NOT CURL_DISABLE_INSTALL AND BUILD_SHARED_LIBS)
     install(TARGETS ${LIB_SHARED}
       EXPORT ${TARGETS_EXPORT_NAME}
       ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}

src/CMakeLists.txt

@@ -141,8 +141,13 @@ endif()
 
 ################################################################################
 
-install(TARGETS ${EXE_NAME} EXPORT ${TARGETS_EXPORT_NAME} DESTINATION ${CMAKE_INSTALL_BINDIR})
-export(TARGETS ${EXE_NAME}
-  FILE "${PROJECT_BINARY_DIR}/curl-target.cmake"
-  NAMESPACE ${PROJECT_NAME}::
-)
+if(CURL_ENABLE_EXPORT_TARGET)
+  if(NOT CURL_DISABLE_INSTALL)
+    install(TARGETS ${EXE_NAME} EXPORT ${TARGETS_EXPORT_NAME} DESTINATION ${CMAKE_INSTALL_BINDIR})
+  endif()
+
+  export(TARGETS ${EXE_NAME}
+    FILE "${PROJECT_BINARY_DIR}/curl-target.cmake"
+    NAMESPACE ${PROJECT_NAME}::
+  )
+endif()