Clarify /DEBUG defaults

Simplify discussion of option behavior, and gather default behavior info into a single paragraph.

Author: Colin Robertson

docs/build/reference/debug-generate-debug-info.md

@@ -57,14 +57,14 @@ The linker puts the debugging information into a program database (PDB) file. It
 
 An executable (.exe file or DLL) created for debugging contains the name and path of the corresponding PDB. The debugger reads the embedded name and uses the PDB when you debug the program. The linker uses the base name of the program and the extension .pdb to name the program database, and embeds the path where it was created. To override this default, set [/PDB](../../build/reference/pdb-use-program-database.md) and specify a different file name.  
 
-The **/DEBUG:FASTLINK** option is the linker default for debug builds in Visual Studio 2017, set when you specify /DEBUG with no additional options. This option leaves private symbol information in the individual compilation products used to build the executable. It generates a limited PDB that indexes into the debug information in the object files and libraries used to build the executable instead of making a full copy. This option can link from two to four times as fast as full PDB generation, and is recommended when you are debugging locally and have the build products available. This limited PDB can't be used for debugging when the required build products are not available, such as when the executable is deployed on another computer. In a developer command prompt, you can use the mspdbcmf.exe tool to generate a full PDB from this limited PDB. In Visual Studio, use the Project or Build menu items for generating a full PDB file to create a full PDB for the project or solution.  
+The **/DEBUG:FASTLINK** option leaves private symbol information in the individual compilation products used to build the executable. It generates a limited PDB that indexes into the debug information in the object files and libraries used to build the executable instead of making a full copy. This option can link from two to four times as fast as full PDB generation, and is recommended when you are debugging locally and have the build products available. This limited PDB can't be used for debugging when the required build products are not available, such as when the executable is deployed on another computer. In a developer command prompt, you can use the mspdbcmf.exe tool to generate a full PDB from this limited PDB. In Visual Studio, use the Project or Build menu items for generating a full PDB file to create a full PDB for the project or solution.  
 
-The **/DEBUG:FULL** option is the linker default for debug/release builds in Visual Studio 2015 and release builds in Visual Studio 2017, set when you specify /DEBUG with no additional options. This option moves all private symbol information from individual compilation products (object files and libraries) into a single PDB, and can be the most time-consuming part of the link. However, the full PDB can be used to debug the executable when no other build products are available, such as when the executable is deployed.  
+The **/DEBUG:FULL** option moves all private symbol information from individual compilation products (object files and libraries) into a single PDB, and can be the most time-consuming part of the link. However, the full PDB can be used to debug the executable when no other build products are available, such as when the executable is deployed.  
 
 The **/DEBUG:NONE** option does not generate a PDB.  
-
-Notwithstanding the above comments, the **/DEBUG** option (with no additional options) defaults to **/DEBUG:FULL** when you use the linker outside the Visual Studio IDE, e.g., in the command prompt or in a Makefile.
-
+  
+When you specify **/DEBUG** with no additional options, the linker defaults to **/DEBUG:FULL** for command line and makefile builds, for release builds in the Visual Studio IDE, and for both debug and release builds in Visual Studio 2015 and earlier versions. Beginning in Visual Studio 2017, the build system in the IDE defaults to **/DEBUG:FASTLINK** when you specify the **/DEBUG** option for debug builds. Other defaults are unchanged to maintain backward compatibility.  
+  
 The compiler's [C7 Compatible](../../build/reference/z7-zi-zi-debug-information-format.md) (/Z7) option causes the compiler to leave the debugging information in the .obj files. You can also use the [Program Database](../../build/reference/z7-zi-zi-debug-information-format.md) (/Zi) compiler option to store the debugging information in a PDB for the .obj file. The linker looks for the object's PDB first in the absolute path written in the .obj file, and then in the directory that contains the .obj file. You cannot specify an object's PDB file name or location to the linker.  
 
 [/INCREMENTAL](../../build/reference/incremental-link-incrementally.md) is implied when /DEBUG is specified.