Cmake include header only target from header only

Question

I'm trying to setup cmake so that I can have a header only library that depends on another header only library. My directory structure looks like this.

library_a
|_a.hpp
library_b
|_b.hpp
library_c
|_c.hpp
|_c.cpp

I have my CMakeLists.txt setup as follows

Directory root:

add_subdirectory (library_a)
add_subdirectory (library_b)
add_subdirectory (library_c)

library_a directory

add_library(target_a INTERFACE)
target_sources(target_a INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/a.hpp>)
target_include_directories(target_a INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>)

library_b directory

add_library(target_b INTERFACE)
target_sources(target_b INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/b.hpp>)
target_include_directories(target_b INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>)
target_link_library(target_b INTERFACE target_a)

library_c directory

add_library(target_c STATIC)
target_sources(korc_node_context
               PUBLIC    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/c.cpp>
               INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/c.hpp>)

target_include_directories(target_c INTERFACE $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>)

target_link_libraries(target_c INTERFACE target_b)

Target library_a is meant to be the generic interface to the library_b implementation. Eventually there will be more implementations. So in c.hpp I include the a.hpp header and use b.hpp in the c.cpp implementation. Everything configures fine but when I go to compile, I get an error that the a.hpp file cannot be found. How can I get target_link_libraries(target_c INTERFACE target_b) to include the headers from target_a?