build: tidy up compiler definition for tests

- tests: merge cmake commands.
- tests: use `target_compile_definitions()`.
- tests/server: use generator expression for platform-specific macro.
- tests/unit: sync `Makefile.am` comment with cmake.
- tests/unit: merge two `AM_CPPFLAGS` lines to keep synced with cmake.
- tests: move macro definitions to `first.h` headers from build level.
  `CURL_NO_OLDIES`, `CURL_DISABLE_DEPRECATION`, `WITHOUT_LIBCURL`,
  `CURL_STATICLIB` (for servers).
  To share more logic.
  Pass `CURL_STATICLIB` in server on all platforms for simplicity.
  (On non-Windows, it's a no-op. It's already done like this with curlu
  and libcurltool.)

Also for lib:
- lib: merge commands.
- lib: sync macro order with tests (also in `Makefile.am`).

Closes #17768

lib/CMakeLists.txt

@@ -24,8 +24,7 @@
 
 set(LIBCURL_OUTPUT_NAME "${LIB_NAME}" CACHE STRING "Basename of the curl library")
 
-set_property(DIRECTORY APPEND PROPERTY COMPILE_DEFINITIONS "BUILDING_LIBCURL")
-set_property(DIRECTORY APPEND PROPERTY COMPILE_DEFINITIONS "${CURL_DEBUG_MACROS}")
+set_property(DIRECTORY APPEND PROPERTY COMPILE_DEFINITIONS ${CURL_DEBUG_MACROS} "BUILDING_LIBCURL")
 
 configure_file("curl_config.h.cmake" "${CMAKE_CURRENT_BINARY_DIR}/curl_config.h")
 

lib/Makefile.am

@@ -66,7 +66,6 @@ AM_CPPFLAGS = -I$(top_srcdir)/include   \
 # Prevent LIBS from being used for all link targets
 LIBS = $(BLANK_AT_MAKETIME)
 
-AM_CPPFLAGS += -DBUILDING_LIBCURL
 AM_LDFLAGS =
 AM_CFLAGS =
 if DEBUGBUILD
@@ -75,6 +74,7 @@ endif
 if CURLDEBUG
 AM_CPPFLAGS += -DCURLDEBUG
 endif
+AM_CPPFLAGS += -DBUILDING_LIBCURL
 
 if DOING_NATIVE_WINDOWS
 CSOURCES += dllmain.c